Drop chain into the small ring at the front and the little cog at the rear. Release the brake release lever, release the QR lever on wheel, push the rear mech back and down (straightening it sort of) while lifting the bike up, the wheel will drop out, move the frame to the side so the wheel becomes clear of the chain and you are done! This is the cleanest and fastest way to get the wheel out, gravity works in your favour with relation to keeping the chain out of the way. To put it back in do the same in reverse, lower the frame over the wheel making sure the cassette goes into the chain loop, lower the frame down so the chain is seated over the smallest cog, lower it right down until it settles, sometimes it will go right into place, other times it will sit somewhere close but not quite right, if the latter, make the same movement to the rear mech as when removing the wheel, the frames own weight will cause it to drop down over the wheel seating the wheel, check it is seated by pushing down on the saddle and then tighten the QR and close off the brake release.
If the QR lever is hitting the mech, it is in the wrong way, the lever should be on the non-drive side!