What you should do depends on the cause. And if deleting an item makes any difference totally depends on what kind of item it is, so it's quite possible that it didn't have any effect.
Generally, unless it's hardware like a detoriating hard disk, going back to factory conditions makes it just as fast as it was when it was new. So I'd start with checking the hard disk with the makers diagnostics or Crystaldiskinfo (free download).
If you go back to factory conditions, you'll lose your data. Make sure you have a good backup.
Im new here. This is my first post, hope to be given your advice.
My laptop is running so slow event I deleted all unnecessary items
What should I do now