I want to change out my u joints how hard is this to do and is there anything I should know when doing it

Pulled this link from Acks Faq, should give you all the info you need.

I recommend spending the extra money on OEM U-joints or the Mitsubishi ones from Trail Tough.  The Napa ones just tend to destroy themselves before their time.

http://www.izook.com/tech/samurai/drivetrain/ujoint/ujoint.htm

That installation link is good and all but a vise works way better than any hammer. I've chased too many needle bearings trying it with out it. I paid to have it done for years because I kept screwing them up. After watching several methods, I can now do it myself with a vise, snap ring pliers, lead hammer and small screwdriver and sockets for pressing in the bearings. Word of caution, be very carefull not to let one of the needle bearings fall down. If it does, the joint will be tight and you won't be able to get the second snap ring on. Oh yeah, I get my u-joints at Autozone. Only $ 8.99 and the needle bearings are longer than the ones I took off that I believe were oem.