Raising water level in toilet bowl Niagara Stealth

the seal between the tank and seating would be the problem or a crack in the same area

water level in the bowl( pan) is determined by the height of the sewerage pipe level that it is connected to and is fixed by design and style of the pan
unless you are on about the water level in the cistern( tank) which you can adjust yourself

Turn knob on top of float ball to increase ball height which will increase water column. Up to 1" of overflow tube.

Make sure the fill tube in the tank from the fill valve is in the overflow tibe inside tank. The tube allows bowl to fill with water to correct level.

Water Level Adjustment
1. To adjust, simply turn upper half of valve counter-clockwise to unlock, pull up till water line on valve is level with water line marked in tank, Fig.C then turn clockwise till valve snaps into locked position.
2. Turn on water supply to fill tank.
3. Tamper proof key is optional, and may be used to simply to prevent further adjustment once final setting is achieved. Fig D

Too little water in the toilet bowl to start with may be due to a lost or mis-connected fill tube that directs some water into the toilet tank standpipe (and thus into the bowl below), while the toilet tank is being re-filled. Check for that little tube.

Check the web site out below for more information on this topic.

http://www.inspectapedia.com/plumbing/Toilet_Slow_Flush.htm

I don't know what kind of toilet you have, but if it has a tank, then probably the tube that squirts water down the pipe into the bowl has come out. Take the top off the tank and as you watch, flush the toilet and make sure water is going thru the tube down into the pipe. good luck

The water level in the bowl is limited by the height of the internal trap down stream from the bowl. There is no adjustment possible. If the problem is odors, you can either flush more often, turn on the exhaust fan, or buy a different brand or model of toilet.