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That should have been a clue. Next time, just run the Disk Cleanup.

I've never tried deleting those files manually, so I can't predict the results. If you'd rather go that route, that's your call.

This is how I usually do it:
Right-click on C: drive, and click...

You should log in as an administrator when you run the disk cleanup. If not, you'll see a "Clean up system files" button, but that's about it. You don't need to take ownership or run commands.
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C:\Windows\Winsxs isn't just the SP1 files. It contains old Windows Updates files as well. SP1 was released in 2010, so I highly doubt you'd want to roll it back.
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I'm assuming you mean "Service Pack Backup Files". The files would be in the C:\Windows\Winsxs folder, along with other Windows Updates files.

Unless you are planning to roll back out of SP1,...