need to change washers on sink. can't turn off water under sink?

Shut off water at the main, where the water enters your home. This will allow you to work on the sink.

Technically, you should have those valves replaced too.

But, the easiest way out of this is to shut off the main water to the house and change the washers out (If you even have to. You don't need to shut off the water to change the washer at the outlet of the spout).

Messing with those valves with a wrench or anything will cause them to break if they are frozen due to hard water corrosion.

First, shut off the main water supply to the house. Second, got to the lowest level and open the faucet ( this usually in the basement) or the out side faucet. By opening the faucet you allow the system to drain.

Once the water stops flowing out of the faucet you may proceed with your washer replacement. What I would do since the water is off is replace the shut off valves. Forget the wrench, cut them out and replace them.

Wash the valves in hot water and cleaner (one of those lime, scale and rust removers from the hardware store) to disolve the mineral deposits and the valves should turn just fine

Try loosing the nut below the handle.

you could always turn off the master water intake ...check your basement/cellar

shut off your hole water supply