When you lose your keys and don't have a spare set, the only option is to remove the door lock and replace it with a new one. Changing a lock can be straightforward or extremely difficult, depending on the type of lock and whether you can get inside the room. Buying a new lock of the same type will help to cut down installation time.
Break off the door handle if you can’t get into the room with the useless lock. You can only remove the lock from the inside. If you have a door knob with an inset lock, or a lever handle lock, use a lump hammer to bash off the handle. If you don’t have a lump hammer, anything heavy will do; for example, a brick.
Look inside the exposed shaft of the handle, or the hole where the lever handle used to be. On a door knob you will see two prongs pointing towards you. Stick your flat-head screw driver between them and turn it to the left. The lock should turn and open. If it doesn’t, turn it to the right. If you don’t have a flat-head screwdriver, use a standard dinner knife. The lever handle will have a metal bar that fits into the back of the handle. This may have become deformed when you removed the handle. Grip the bar with the pliers and turn it; try turning to the left and to the right.
Examine the lock on the back of the door. If you have a lever handle lock, it probably includes a plate, and the plate on the handle on the back of the door will have visible screws. Unscrew them, pull off the handle, and then slip out the bar that runs through the interior mechanism. If you have a door knob, look closely at the side of the shaft to find the small hole. Open the pack of your new handle and take out a small plastic box containing the screw. This will also have a small flat metal device that has a round head and a point at the other end. Stick this point into the hole and pull off the handle. Unscrew or prise off the plate to expose the screws. Unscrew these and then the two sides of the handle will come away.
If the bolt in the side of the door is not damaged, don’t bother taking it out. Just fit the new handles into the internal mechanism.
When you go to the DIY shop to buy a lock, also buy a couple of spares for the next time you lose your keys.