If you are just sticking to the same tuning and strings then they are a piece of cake!
Just undo the bolts on the nut and start turning the tuner for the first string to take away the tension.
Now follow that string down to the bridge, its sitting on a piece of metal, thats called the saddle, now at the back the is a allen key bolt going into it, thats pressing up against the string and keeping it in there.
Simply undo that and pull the string out, grab a new string and chop the ball end off, chuck it back into the saddle and tighten, you don't need to put loads of strength into tightening it or else you might break it.
Now that the string is in the saddle and secured wrap the other end around the tuner peg and tension it up.
Continue doing this for each string until you have finished, then get it in tune, tighten the bolts down on the nut and use the fine tuners on the trem to correct any strings that are out of tune.