i got my car checked and said need new distributor cap and rotor.
1 How hard is it to change?
2 Do i need to put a new o-ring when i change it? heard you do but idk

 

When you buy the cap and rotor they usually come with a new o-ring/cap seal. It's a fairly easy job to do. there are 3 screws on the cap and one on the rotor. The Philips screw on the rotor shaft may require you to turn the engine over a bit to get the screw lined up with the opening in the dust cover. you can ether do this with the ignition or manually rotating the crank.

Make sure that when you remove the spark plug wires from the cap that you do it one at a time and put them in the same spot on the new distributor. Or at least document what one goes where.

 

What GhostAccord said.