My 1990 bmw 535i is overheating and i changed the rad and its still over heats and the can blows heat just on the top vents of dash and not on the lower dash vents

no, not special but you failed to stated engine, there are many engines.
and some are very tricky here, like 2.0L.
First state the symptoms,
your post states its overheating, then no heat. (why?)
old post. but others might
Ill post , overheating ,
Example if me, with overheat.
I see my dash gauge, show overheating and engine power drops and pings, then steam vents from the rad, cap?
Over heating (ill skip cab heater but on 2L this path blocked causes thermostat to go quite nuts. not posting engine, makes this hard.)
1: full of 50% AF (antifreeze)
2: new thermoSTAT they age and fail fast. so get a new one.
put STAT in with the wax slug down, and jiggle bleed pin forward.
get air out of system after filling, (RTM)
start car, and....
4: then using and IR pyro gun we then check that
the thermostat housing hits 170F min. but not too hot.
run motor till top rad hose gets too hot to touch 180f is normal.
I had to drive 10 miles, to get it up to 180F.
my car has the hotter, 195 STA,T so runs at 195f. (helps cooling)
USING the pyro gun , the top and bottom of each rad tube.
This tool is Amazing.... and saves burn hands.
if the bottom of any RAD tube is way less than the others?, that is
a clogged UP rad tube. solution is , NEW RAD.
Usually rad repairs, are more costly than new. IN USA.
The water pump must spin at full speed, belt tight.
The impeller or some suz, motors likes disappear. from electrolysis action. so not looking at the impeller is a FAILURE on the mechanic side.
if this car has 2.0 I-4 (4 banger) it has a coolant tube on the rear
of the STAT housing, this tube must flow coolant at all times.
if it dont, the thermostat , will go nuts.
nuts means, that insufficient flow passes the thermostat wax block
causing the thermostat to cycle in a wild and random way.
I dont like this design but is reality. If applicable.
post country, post engine type and state the symptoms.

Sounds like U need to purge the trapped air out & possibly change the thermostat & see if that worx....( you didnt mention if U replaced the radiator)

It may be a problem with your vent control system in your dash. You have a vacuum supply that comes from the top of your engine and travels through your firewall and under your dash to be used to activate the movement of your vent controls. If you have a break in this vacuum line, your vents will not move to change from cool to hot air regardless of where you put your control dial.
That could be your problem.......... or your heater core could be plugged. The core is a mini rad that is under your dash. It takes in hot engine coolant and acts as the heat source. This mini rad sometimes plugs up from ordinary use. Deposits slowly gather up and eventually clog up this rad making it useless. This rad may need to be replaced. Even though your pipes going under your dash are hot, the flow is probably very very slow and not giving enough flow to create heat for you inside your car.
You maybe able to flush out the mini rad by waiting till the engine is cold, then disconnect both hoses under the hood going under the dash, blow out most of the coolant remaining in the heater core(if you can)( also be careful of your eyes) then block one of the lines and put some rad flush through the other line(use a funnel with a hose attached). Leave it there for a while then try running water through it with a garden hose. Be careful to not splash the rad flush fluid in your eyes(wear safety glasses and also wear gloves. Repeat if you feel. Try to flush out as much of the rad flush as you can before reattaching the hoses. Remember to add some coolant cause you will lose some. It would be better to add coolant to the heater core before you attach the hoses to get most of the air out of the system. Good luck

check fuse to blower motor under dash you may have a bad blower motor

your cars radiator hose is building excessive pressure because the coolant / water could not circulate freely on your cooling system thats why its overheating, try removing the thermostat valve first and observe if it makes a difference, if problem is the same it could be the water pump is the culprit. try eliminating the easy things and less expensive approach first before deciding to top overhaul the engine of your car. a broken head gasket is not enough reason wont blow off your top radiator hose.

Your relays are or should be in the engine compartment under a plastic box or under the dash board on the driver's side or on the side of the dash board on drivers side.
I use to own a 2003 BMW 325i sweet cars

it may have a blown head gasket if it keep over heating or there could be just an air lock in the cooling water,, you will need to bleed the air out to stop the over heat as the water is not going around the engine its not opening the thermostat so it cant bleed its self take off a water pipe thats the higest pipe you can find it may have a bleed vent in a pipe were you can bleed it from ,,,top up the rad and header tank take off the bleed nippel when water with no air is coming out and the jobs a good un? run the motor for a time or go for a drive to check its not ever heating again and the heater should by now be blowing hot air,, top up the rad and header tank when its coold down

It could possibly be the cabin air filter is clogged, especially if it has never been changed. Aside from that it is probably one of the stepper motors that adjust the various vent gates in the air passages under the dash. Although replacing the cabin air filter on this car is fairly easy, comparatively speaking, you do have to remove the glove box in order to do it.

Yes, you re correct! thats a thermostat issue.

Have you checked your rad fans? Rad flow? Rad condition? Possible water pump problem if those check out good.