No repair less than replacement will be reliable.

Remove and replace.

I am new to plumbing and would like to learn it. Any easy way to remove it? I know I can cut it but I am afraid that the it will shorten the remaining water pipe that comes off the wall. Someone told me I can 'heat' the joints and the valve will just come off?

You can heat the joints, but you have to make sure there is no water in the line or you will be unlikely to get it hot enough to melt the solder out.

Is there another valve before this one that can be closed to then this section of pipe drained?

The diameter of the pipe (and thus the mass of the valve) will drive how large a torch will be needed.

For this repair, it would be advisable to just hire a plumber and observe. (You might want to pick up a replacement valve before the service call.)

Thanks brickeyee. The pipe inside the wall has shut-off valve and I can be sure that there will be no water coming out during the operation. The diameter is one inch.

" The diameter is one inch."

One inch pipe takes a decent size torch (or tip if you can change them).

Likely more than a little LP bottle of the Bernz-o-matic size.

Unless you have a future need for a larger torch, this might be worth hiring out.