How do I change a washer in a bathroom sink shut-off valve

Shut off the main water S/O valve, open your sink faucet to drain the water, open the angle valve all the way, remove the packing nut, remove the valve stem assembly, remove the screw at the end of the stem, see the image below and you be able to remove the washer, get a new one and replace it, Good luck.

John

John's advice it very correct. However, if you have not done small jobs like this you can replace the entire stop for about $5.

If you decide to replace the angle stop you don't have to remove the large nut and ferrule on the 1/2" copper stub out. Simply reuse them. Good luck, Tom

If you decide to change the valve assembly as Bob suggested see the image below, Thanks.

John