Depending on the style of the new seal. 1st, take out the drive shaft. May loose some fluid when doing this so be prepared. If it mounts flush inside the tailshaft, take a screwdriver and working in a circular mannor, pry the old seal outward. Clean the surface and tap the new one in with a soft faced hammer if you have one. A regular hammer will work if not. Knock it in, in a circular motion as well until the seal is in flush with the tail shaft.
If the old seal has a lip that mounts flush to the outside of the tailshaft, take a screwdriver and a hammer and working between the lip and the trans knock the screwdriver in, working around the diamiter of the seal to pull the lip away from the tailshaft and then wedge the screwdriver inside the seal and pry it out. Istallation is the same as above. Put the drive shaft in and check your fluid level.
to check to see if it is full, unscrew the top bolt, just get a 3/8 ratchet and stick that in the bolt. it is on the pass. side. if fluid comes out then it is full if the car is level. to drain just take the bottom plug out and to refill pour the new tranny fluid into the shifter casing.