After you remove your mattress and box spring from your bed frame, turn the entire frame assembly upside down. Remove the old feet by just pulling them out of their sockets, using pliers or wrenches if you need additional leverage; once the feet are removed, pop the new feet into place. For feet that screw into the frame, unscrew the old feet and replace with the new bed frame feet.
Some bed frame feet, particularly those with heavy-duty casters or rollers, have tapered steel bars that connect to the inside of the bed frame and make removal more labor intensive. In these cases, attempt to free the problem foot by using a wrench or pry-bar. If this technique does not produce results, spray a metal lubricant into the socket to loosen any rust, then try removing the foot again. If this still fails to produce results, enlist the help of a few friends to stand on the frame while you pry the stubborn foot loose.
Other types of bed feet insert most the foot's body into the frame's socket, making standard removal methods difficult. In these cases, attach an adjustable wrench or pair of channel-lock pliers around the exposed part of the foot and pull and twist until it comes free.