You can replace your sliding patio door handles. This is not a very difficult task and can be done quickly. The same types of handles are made by virtually all manufacturers, so it should just be a simple matter of removing one handle, and replacing it with another.
It's also easy to replace your sliding patio door handles with a lock and handle system. While it is much easier to replace your sliding patio door handles with handles that are exactly the same, you can also try using different replacement handles, which may need a few holes drilled in the door to improve it.
Step 1 - Remove the Old Handle
Open the door so that you can remove the old handle of your sliding door. You can do this by sliding it back, but it is a good idea to keep it open with a large brick, or one of those devices that holds a bike's wheel in place. You should secure the door so it can't be pulled shut, and then take off the handle.
You should find a few screws around the edge of the handle, which need to be unscrewed, or you may have a screw on the edge of the door frame. Remove these screws and the handle should simply fall off. You may need to pry it off with the edge of a flat-headed screwdriver if it has been on the door a while.
Step 2 - Calculate the Size Needed
Measure the hole you now have in your door. You should take notes of the width of the lock needed, along with any specific pattern of faceplate. You can then calculate the distance between each of the mounting screws. You may also want to make a note of the handle maker, but don't forget that you need to know the maker of your door. This should not be very difficult to find out, and you can then calculate the right size of replacement sliding patio door handles.
Step 3 - Fit the New Handle
Once you have your new handle, you can then fit it to the door. If you have a surface mounted handle, in that the screws are on the face of the door, then this should be easily fitted, although you may need to drill new holes to get the screws to line up correctly. For a mortise lock, you may have more problems.
Push the lock into the frame, and then fit the mortise rod. You should then be able to slide the screws into the same hole as before, and push the lock into position. If you need to drill a different hole to fit the rod, make sure that you seal the other hole over with putty, or something similar, in order to protect the door.