I have a 240 plug next to my Ac and was wondering if I could have the plug changed to 115 plug so the AC in the window can run off that plug instead of extension cord leading to another plug in the house

Sure, one of the hots will need to be reidentified and reconnected as the neutral, then install a 120 volt outlet, and 20 Amp single pole breaker. 15 amp breaker if #14 wire.

Ty heaps