An important part to not screw up is when removing the seals, be extra careful not to scratch the bore in which the seal will call home.
A lot of people use a straight screwdriver and work their way around the seal a little at a time to gradually pry the seal out. You can also buy a seal pull for less that $10, but I've never used one.
Wipe the seal bore clean and then take your finger to rub a small amount engine oil around the seal bore. Also, lightly coat the new seal with oil and this will help the seal go in smoothly. A large socket or piece of PVC pipe that is about the same diameter of the seal is good driving the seal in square. I just take a socket, piece of wood, and hammer and slowly tap the seal in. They also make a seal driver kit for cheap, again, I've never used one.
If you really don't trust yourself, here is a link to the tool I mentioned above, but are not necessary for this job. Good luck.
Lisle Seal Puller $6.99
Craftsman Seal Puller $9.99
Snap-on Seal & Bushing Driver Set
^ You can find these really cheap and www.harborfreight.com