actually, the odors could be coming from the leaking flange seal too... don't ask me how I know! To pull the toilet, there should be two to three bolts holding the toilet to the black tank. Remove those (the back one is hardest to reach), and the toilet should lift right up (drain that toilet first!). Depending on how much slack on the water supply hose, you may have to disconnect that first.
Get a new rubberseal from an RV supply store, bolt it back on, and you're done! Use new teflon tape on the water supply hose if you don't have a compression type connection (i.e. - if there is a taper on the male side of the connection, don't use the tape).