We have a window in our kitchen that looks into the den, and it seems like the previous owner
When installing the window had a support beam put in just above the top of the window.

This is where the problem lies, the support beam is very poorly blended with the rest of the wall and seams to look like a section of the wall is bulging out. What would be the best way of repairing this.

I was thinking to patch it all the way to the ceiling and then sand it down.

Any other suggestions.

Can you take a pic and post it?

May try and use some sheetrock mud and float the bulge out, try using a 10 or 12" sheetrock knife and put a few coats on and see if you can blend it in better.