My water heater is leaking from the top around the copper fittings. It seems to be filled to capacity.
Will adjusting my pressure relief valve stop my water heater from leaking? I turned the main water valve off. I also opened the faucet near bottom of tank to drain.
Water heaters do not live forever. Start shopping.
While it is possible that you have a leaky fitting near the water heater, (which could be fixed) the most common cause for a leaky water heater is that the water heater itself has started to fail, and the only option there is replacement, as the corroded tank is not a replaceable part.
Depending where you are, there are some pretty good deals on more-efficient water heaters available in some areas.
Most temperature and pressure relief valves are not adjustable, and in any case the pressure inside should just be the water pressure of your house, so if you could lower the relief pressure, it would leak all the time.
By design it is always filled to capacity, it is a pressure tank. Do not mess with the relief valve, it is there to prevent the tank from exploding due to malfunction causing overheating (if you are curious about that just do an internet search of boiler explosions). Do not turn off the water supply and drain the tank without also turning off the heat source (electric or gas, by the way?).
As @ecnerwal states, you (or a plumber) should be able to determine if the fittings are leaking and repair them if they are. If the tank itself is compromised you need to replace the whole unit.
