How to make my screen bigger while playing a game?

Every time I open a pc game for some reason it's in a smaller window, not full screened. It's never happened before, I don't know what the problem is. My laptop used to automatically make games full screen, and now it just stopped. I tried changing my screen resolution, but that didn't work. And most games I play don't have an option on what size I want the screen to be. Any idea on how I can fix this?

Thanks.How to make my screen bigger while playing a game?Either press an expand window button if there is one or drag out the bottom right cornerHow to make my screen bigger while playing a game?try clicking f11, if not then i dont know, but what games are they first. like internet games, downloaded, or disc ??