Normally no. ResMan will apply them automatically for you once a charge exists.
It will apply the credit using the same payment priority option that it would have used when entering a payment...which was setup by your administrator.
If you run your Aged Receivable report at month end, and you see a charge and a credit that should be applied together, go to the resident's page and click Apply Available Balance (in the Accounting > Action menu). Date: Use the most recent of the charge/credit dates to apply them.