Can place Overclockers (O), Energy storage (B for battery I assume?), transformer (T), and an upgrade that allows machines to run off of MJ (M) instead of EU by right clicking the machine with the upgrade in your hand. I don't know how to remove the upgrades, but you can view what upgrades a machine has by using the portable scanner.
A quick search should go into more explanation on how overclockers affect EU draw and processing speed. The decrease in efficiency becomes pretty substantial as you put in more overclockers, so be careful.