Depending on the source of the problem, fixing an oven door may include replacing the hinges, switching out the springs or changing the gasket that lines the door. These fixes generally can be performed by the homeowner.
Begin by unplugging the oven to avoid the risk of getting shocked, and turn off the gas if the oven is a gas model. Remove the oven door by pulling it up and outward to release the hinges. If it does not come off, check for screws that may be securing the hinges, and remove them. If the hinges appear damaged, replace them with identical hinges and hook them back into the oven's hinge holes. If the hinges are intact, check the door springs by taking out the bottom drawer and examining the bottom of the oven. Use pliers to remove the bolts from a broken spring, and replace it with a new, identical spring. Keep in mind that not all oven models have springs.
The rubber or silicone fabric gasket may also be causing the oven to close improperly. Pry the gasket loose using a flat-head screwdriver, and replace it with a gasket of identical length by pressing one end under the groove of the door and continuing to the other end. When purchasing replacement parts, have the broken parts or the oven's model number on hand to find an appropriate match.