Replacing a pinion seal in a 51 dodge?

I think I've found the seal just can't figure out how the hell to get the old one out and the new one in also do I need a special tool and where do I get one?

 

take two flat blade screw drivers and place them on both sides of the seal and pound them in with a 16 ounce hammer with a fiber glass handle to reduce shock from the recoil into your rist and pop the seal out!! ive done it a 100 times why didnt you ask me !!! i got two 99 cent flat blade screw driver's ill sell you for 20 bucks it should do the trick!! hahahah i just had to fuck with you !! no but if andbody really knows how or what to do help my pops out!!

your son timmy!