If you like your trusty watch but a part is not working correctly or the battery is dead, you need to take apart the watch to get inside and replace the bad part. There are many different kinds, makes and models of watches and many ways to assemble and disassemble them. This may sound discouraging. But the good news is that the fundamentals of all watches are basically the same.
Examine the watch. If possible, figure out the type of watch it is and how it works. Do not take it apart unless you are sure you know how to put it back together. It may also be a good idea to get something to secure the watch or hold it down while you take it apart.
Unscrew the screws with a screwdriver. Place them in a container so they will not be lost. Be careful not to bend or break these screws. The screws are replaceable, but you risk bending or breaking other smaller parts that may not be. Also, if the screw will not turn, do not force it. You risk stripping it; it is then virtually impossible to remove the stripped screw.
Remove the battery. Be sure not to leave fingerprints or any other marks, including scratches. Also, be very careful not to bend the metal. Batteries can be expensive to replace if damaged. Keep this with your screws and other parts.
Take out all springs and screws that might be contained inside your watch. Keep them safe and be sure not to damage any parts. Remember: it is never a good idea to force or pry anything apart. If the part does not want to come out, leave it.
Reassemble your watch. Make sure you put everything back properly without bending or leaving fingerprints. Test your battery while your watch is disassembled to avoid having to take it apart again.