If it is a Thetford brand they have "how to" info on their web site. The model I have has to be removed from the floor (two nuts) and then you can access the bolts inside that allow the front to slide off where you can get to the gasket. It is easy to do and doesn't take long. The floor gasket should be replaced when you put the toilet back on the floor unless it is pretty new.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof