After the win 10 upgrade, everything has been slow, and I can't figure out why but don't totally care right now. More importantly I only have 35GB left on a 250GB partition for c: I'm not the absolute most knowledgeable in computers, but I was trying to fix the slow issue and came across that the file folder marked windows.old is something to do with win 8.1? Do I need this massive 35GB folder? Because that would double the space I have left just by not needing it. I don't understand what the folder itself contains, or if it's important, what its use would be in the future etc. Help appreciated, please.