First, replace the ac filter if its clogged.
after that just turn the blower on, don't push the AC button, how does the airflow feel? change blower speeds, does airflow increases with blower speed? if it okay, then i think the evaporator is okay and donot require service. but if you feel that airflow is kinda restricted then get the evaporator services, which might require refilling of refrigerant etc.
after checking that get the both low/high pressure checking from reliable AC technician, if found out of range then adjust the refrigerant pressure accordingly...