Cannot remove holes from a model

I'm trying to figure out how to remove these holes from the sides of a model as it will only allow me to delete certain ones, while saying others can't be deleted. I've tried using feature recognition many, many times, and it usually just freezes, or freezes for about 20 minutes, then says it can't recognize any features. It's gotten extremely infuriating as nothing seems to work. Any help is much appreciated

SolidworksParts And Features