My tub is=leaking I know it needs new washer but not sure where to go to get into it to replace washer I have a old model it has one knob. And the hot/cold is also on the knob. To gauge temp for water please help so I can stop leak thank u

My tub is=leaking I know it needs new washer but not sure where to go to get into it to replace washer I have a old model it has one knob. And the hot/cold is also on the knob. To gauge temp for water please help so I can stop leak thank u
This is a older Delta bath and shower valve, (see image) REplace the seats and springs, While you have the valve open turn the water back on to flush out the supplies, Good luck. Tom