How to replace plastic blades on a challenge mower

A riding lawn mower typically has a lever that adjust about 5 different heights. The manual to the mower should indicate how to adjust the ride height.

As you have not identified brand and model, useful also in finding a manual online, it is a bit challenging to describe the process, although it is actually too difficult to perform. Below the deck where the blade is attached is likely a cotter pin. If that is extracted, the blade height may be adjust with the adjustment wheel. Subsequetly, the pin is replaced. It may be necessary to adjust the "level" of the blade as if tilted, an uneven cut may result. Removal of the cotter pin may require pliers.

this link might help you out,or you could also try ebay.
Where can buy plastic blades and parts for Certified Electric Hover Mower...

my search shows that up as a
Rota-twin GR101 mower
black and decker /flymo electric mower type

no picture on the parts list
of the rotating part being metal

two types of blade sets ...says its plastic and just clips on

is that for real ....plastic clip on mower blades


will this work
pull to the larger slot to release the old blade and back to the smaller slot to hold the new blade in place

Well I would say you have a bent blade, a blade has a loose connection to the bottom of the mandrel, or a mandrel bearing is going out. Visual inspection will reveal much, just look under the deck. A bad mandrel may appear to have "runout" when viewed from the top while spinning as contrasted with a good mandrel. Viewing the one in the center while deck is working is going to be a challenge. If you decide to replace a mandrel, do yourself a favor and take a picture of the deck belt before you take it off so you know how it goes back on.

mower, then blade, then plastic part, then metal square washer, then nut

I am not sure what an over reign SLM 1500 is and I have never seen a power mower with a plastic blade but in order to remove the lower belt guard from most walk-behind, self propelled lawnmowers so equipped, it is necessary to remove the blade adapter from the bottom of the engine shaft to allow the guard to slide off.
To remove the blade adapter, tip the mower to where you can spray some penetrating oil on the shaft above it and let it soak for a little while. When you think it has had sufficient time to soak down between the shaft and adapter, set it up on your work bench if you have one available or you can do this on the ground as well. Tip the mower back on the handle bar (this will keep your oil from running out into your air filter and clogging it), secure it in the fully tipped back position, take a small hammer and tap downward on the blade adapter while pulling downward, away from the engine at the same time. Use caution not to strike it so hard as to damage or break it. They usually slide of with just a little bit of effort. Once the adapter is off you can easily remove the plastic guard. When reassembling it, I always use a little anti-seize on the adapter to make it easier to remove next time.

IF is it a square plastic washer with 2 "wings\nocht" in the middle you can find at their servicenters because is a very common part and all the Black&Decker mowers use the same one. It holds the blade so you can thighten the nut.

If it's like mine (MM 875), it has a plastic "clutch" that has little edges on it that broke off when I was chopping sticks with the mower ;-) Went to the local B&D place and got a new one for less than $3.

But now I'm worrying about the nut holding the blade on -- if I try to get it good and tight, the plastic "clutch" spins around off-kilter... Funny how I never even looked at the blade after I bought the mower used, but never worried about the blade being loose and flying off.

Wedge a short piece of 2x4 between the blade and the housing,
turn clockwise to tighten !