they are all different and you don't say what kind yours is. Basically, you shut the water off, take it apart and change the seals or control ball. Best way to ID the part is take the internal parts to a Plumbing store and ask them for a kit or seals for it.
To remove a valve stem you have to do the following
1- shut off the water supply
2- remove the handle
3- remove the escutcheon if applicable
4- open the valve to the half open position so it does not bind
5- use a shower socket for the size valve bonnet for the type of valve you have, Gerber, Savoy, Sterling, etc
Since the home is two story a small indoor air conditioner will not be able to cool the whole house by itself. To get this home to be cool you will need to use a A/C system both upstairs and downstairs.
I doubt its your valve.its sounds like you have a drain or a vent problem ,a drian that's falling backwards or has a slight stoppage will make that noise
remove it and add new plumbers tape and screw back into place.
dissassembe, replace the seals and reassemble
how do i fix a leaky sink
This is probably due to one of two things. Either the arm coming out the wall needs to be resealed with plumbers thread tape (thin white teflon tape) or where the head goes into the arm it may need a new washer. Failing these options, check for cracks.
The mens room at our office building has a leaky faucet. Where can we information online on how to fix a leaky faucet?
Replace it
You can fix a leaky faucet.
duct tape it... yay!
You dismantle it and replace the seal.
you replace it
replace the seals
Brake it down
Replace window seals or if they are repairable you can fix them with silcone, it comes in black to match.
Eventually some waterproof tape will appear at the store. Buy that and put it on the leaky hose. Then put some one in the shower to lower the water pressure. Put some one else on the hose and they will fix it.