I'd say do it yourself if its an electric because its easy and near impossible to screw up,if you have a fender type guitar use the tiny allan wrenches to lower each string separately. if you have a guitar with a tune-o-matic bridge (les pauls have them most commonly) adjust the action by lowering each of the two big bolts on each side of the bridge, it depends on the modal but it should either be two screws or thumb adjusters in which you would simply turn with you hands,however these kind will require you to first loosen you strings because the pressure the strings have on the bridge will make it very difficult to adjust.

I always say a guitarist should do as much maintenance as he/she can with thier guitars and not just to save money but you will even get satisfaction out of making you guitar play better. It's good to get to know your instrument, and hey theres tons of people on this site to help you along the way.