Hex head screw trouble?

Looks like it'll take a standard 5/16 nut driver to remove them. If you don't have one, a 1/4 inch drive socket set with a 5/16 socket should do just as well. If neither of these is an option for you, a pair of vice grips should do it, but you risk tearing them up a bit. It sure helps to have the right tool for the job.

Hope this helps.

Add to the other advice: Pilot hole size can make a huge difference, especially when dealing with hardwoods, such as maple, oak, and cherry. Pine (SPF grade 2X4's from the lumber yard) are not so critical. The pilot should be about half the total diameter of the screw, which means the threads are fully engaged, but not pressuring the wood so much as to create binding when they are driven. Hold up the screw, then align the drill with it: you should see the threads, but not the solid inner part of the screw body. The harder the wood variety, the less of the threads you want in the visible alignment method. Practice holes in a scrap wood can help remove any doubts. Also, you don't mention what kind of slot on the screw. Single slot type (commonly an old school wood screw) are notorious for being hard to manage; whereas a Phillips type are a significant improvement in driving convenience. Use those if you have a choice. (Sidebar; if you're drilling 'deck' screws, those look like a Phillips type, but actually take a square bit drive. Using a Phillips driver will jump out almost every time.)