The rules of no-limit valid also for pot-limit, except for the size of the pot can’t be bigger than the bet.
For example: If a pot is 100$ A player makes a 75$ bet. B Player raises. The raise must be at least 75$, as he can’t raise less than the previous bet. The maximum of the bet is 250$, because after calling 75$ the size of the pot will be 250$ (100$+75$+75$). (B Player must put 325$ into the pot) In this case the pot increases to 500$, and A Player must call 250$ if he wants to stay in the hand.

• If a bet is bigger than the legal maximum, the surplus is given back to the bettor as soon as possible

In computing pot size the little blind is treated as if it were the same size of the big blind. For example, if the blinds are $5 and $10, a player can open with a raise to $40.