Minecraft – Cant delete .minecraft folder for Minecraft

The easy way is to restart your computer and try again. If this doesn't work try to close all apps in Task Manager manually.

The file won't regenerate unless you update Minecraft, and needs to be removed only once for a given version. (If Minecraft has an update and you pick "yes" when it asks if you want to update, it'll reinstall a fresh, new copy of the game, with a brand-new META-INF file and none of your mods.)

The META-INF file is a code signing file. Removing it is necessary if you mod Minecraft because the game will no longer match the code signature, and therefore won't start. Removing it prevents the game from checking if it matches, so then it runs fine.