It could be too tough or, on the contrary, loosened, or simply worn out and outdated, in any case, it will not be difficult to change the door handle yourself. With a few basic tools and following the step-by-step instructions below, you can start removing screws, replacing plates, and trying on the inlet for your new doorknob.
Steps

1 Purchase a replacement pen.
In addition to external beauty, look for something reliable that will withstand everyday use and will last for a long time. Also immediately think about whether this handle will go to the bedroom, bathroom or toilet. Should there be a lock on it? If you have a lever handle and a lock in the core, you should get a left or right handle depending on the direction of the door. Buy a doorknob with a lock that is the same length as the one you are replacing.

2 Remove the two screws on the bezel.
Rotate counterclockwise to pull them out.

3 Remove the two screws on the handle plate.
The handles will loosen, be prepared for both of them to fall.

4 Pull out the handles on both sides.

5 Pull the bezel and lock out through the opening.

6 Loosen the two screws on the panel groove in the wall and remove the panel.

7 Some doorknobs come with multiple bezels.
On this one, you can change the bezel by prying it out with a flat screwdriver. Choose the one that matches the opening of your door.

8 Match the new slot panel and lock with the holes in the door and doorframe.

9 If necessary, use a hammer and chisel to adjust the holes in the door and doorframe.

10 Slide the new lock and bezel into the door.
Make sure the lock faces in the direction the door closes so that the sloped side fits into the groove in the wall. Try to push it through with your hands. If it does not work, you will need to drill a larger hole. Alternatively, you can place a small piece of wood against the faceplate and hammer a little. The black plastic cuff shown in the photo will help remove extra millimeters of diameter if the hole is too large

11 Screw on the lock mechanism, making sure it is as secure as possible.

12 Insert the handles into the door so that the square peg goes into the square hole and the screw holes align with their threads on the other side.
The handles and lock must point in the correct direction.

13 Insert and tighten the bolts that hold the handle.

14 Install the groove panel. 15 Make sure everything fits together and closes securely, if necessary make adjustments.
Advice
- You will need a chair or chair to work at this height, especially if you are working with a chisel. A door stopper or any other item that can be placed to secure the door will also be needed.
- If the old bolts left a lot of sawdust, and it is impossible to screw a new bolt into it, fill these holes with enamel or putty. Let dry, drill a test hole and insert your bolts.
- Read the instructions for your new pen. They may contain useful tips for this particular model.
- If your old metal doorframe groove panel is in fair condition and fits the new handle, you can just leave it on. This part hardly wears out and doesn't get much attention.
- A multi-tool like the Dremel can be used to cut holes and cut off excess wood. You should be very careful. Although working with a hammer and chisel is usually faster, safer and more accurate.
- When all bolts are installed, tighten each one one last time. Sometimes some loosen up when others are tightened. Do not overtighten, especially for wood screws.
Warnings
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DO NOT LOCK YOURSELF!
- Wear glasses when working with a chisel or woodworking tool. Follow the manufacturer's instructions and keep long hair, loose clothing and fingers away from the tool.
- Always follow the basic principles of chiseling: never hit towards your hand, always sharpen the tool sharply and use the correct chisel size. Don't use it at all if you don't know how.
- Most interior doors have a hollow core, which means you won't have a lot of wood to work with. If your lock is too long, for example, you don't have to drill a lot, so work carefully: measure twice and cut once.
- Make sure the handles work on both sides and are seated correctly. Only then close the door!
- Take your time removing wood. It is much easier to remove it than to add it.