Originally Posted by JunkYardBike
Do the the pedal posts have allen wrench recesses? Possibly not if they are cheap, but worth a look. If you have some metric (usually) allen wrenches, they'll do the trick.
Or not. 6mm 'long' Allen keys are about 4" long. 15mm wrenches are about 8" long. If they were put on by a wrench, the pedals will probably be too tight to take off with an Allen key.
Use a 15mm wrench. An actual pedal wrench is the best solution, but they - especially the big Park Tools wrenches - can be pricey.
Do what DannoXYZ says and get a set of metric wrenches.