Before I get into how to replace it, I should ask, does it really need to be
If it is leaking, then it's simple, It needs to be replaced. See
If it is full of water, it needs to be replaced, Tap
the tank the back should sound hollow, if not, it is full. if it is
full, that means it will be very heavy, So be careful not to let drop
on your fingers when you remove it.