The amount you send up to your credit limit will reset every month, but not your actual credit limit. For example, if your statement balance was $2,000 and make a credit card payment of $400, then your new balance is $1,600. If your credit limit is $3,000, then you will have $1,400 to spend according to the payment you made.
Your credit limit will not actually increase though unless you request a raise. The limit will always stay the same from month to month.