Checking Your Settings
If you have a new air conditioner, check the box to see if you bought one that can cool down the space you have. Each air conditioner is only able to cool a specific area, and if your home is too big for the unit, it won't work efficiently. If you have an in-wall unit, set it to reuse the air in your home rather than using the air from outside. Though it would seem that fresh air is nicer, if the machine is pulling in the hot outside air, it won't cool as well as you expect.
Changing the Filters
Air conditioners have a filter that needs replacement every few months. If you use a cheaper filter, you should change it every month, but more expensive filters can last two or three months. Look in your manufacturer's guide to determine the filter size and how to replace it.
Cleaning the Air Conditioner
Air conditioners require cleaning at least once per season. Clear any debris from around the unit that may be blocking airflow. If you have an in-wall unit, you may have covered the back during the winter months and forgotten to remove the cover. Anything preventing airflow can affect the cooling power. Additionally, open the machine and vacuum or wipe down vents or fans in the unit. Always turn off the power before cleaning your air conditioner.
Your air conditioner may have a leak and require more coolant. If you've tried other methods to improve the efficiency of your unit, call a professional to see if this is the case. Or it may simply be time for a new air conditioner. Expect your air conditioner to last only a few years. If you live in a warm climate and use your air conditioner year-round, you will need to replace it more often than someone who only uses the unit in the summer.