Pretty sure that once you get the seat off, there are just two nuts holding the tank. Remove the two nuts, lift and slide back enough to have room to disconnect the fuel and vent lines.
Seat is held on pretty much the same way, except the nuts/bolts are in the tunnel.
2015 Skidoo Renegade BC 600 Etec
1999 Skidoo Summit X 670 HO (Son's)
1996 Skidoo Touring E 380F (sister's)
1995 Skidoo Summit 583 LQ
1985 Skidoo Tundra 250F
1999 Arctic Cat Jag 340F
1999 Arctic Cat Z 370F (son's) - needs track
1990 Arctic Cat Jag 340F
1982 Arctic Cat Panther 440F