Will getting a larger roof A/C solve the problem?

Thanks for all the feedback... when I get home I'll definitely take the outside cover off and look at the fins... adding a second one is impossible in my case.... you've answered my question about the difference in BTUs.. my present unit works okay up until around the afternoon during the summer months.. while home I run the air conditioning all day long with the shades drawn and then the late afternoon I can tell that it just isn't powerful enough to keep the edge off the heat,,, when the Sun goes down and catches up again