As iMac repairs go, this is an easy one, but I do strongly recommend you do it by taking off the bottom case. Yeah, there's some hairy screws in there, but they're all Philips head, and a magnetized screwdriver will do you just fine. The high-voltage stuff is on the other side of the case, as long as you don't decide to go crazy and touch anything you don't want to touch.
It is safe to do it with bare hands, if you take the case off.