Disk Cleanup Questions

I do this regularly, but recently started checking out "Clean up Systems Files" and cleaning up some old stuff. However, I have some huge files on there now that I'm afraid to delete. Some may be connected to my old Windows 7, before I downloaded Windows 10, so maybe they can go. Your opinions would be appreciated!
1. Previous Windows Installation 25 GB
2. Temporary Windows Installation File 4.62 GB
3. Delivery Optimization Files 1.25 MB

Shall I delete them, or will all hell break lose if I do?

 

1 is your previous Win 7 and would be required only if you want to roll back from 10 to 7 during the first 30 days from upgrade. If you are outside 30 days or are certain you want to stay with 10 then it can be deleted. 2 is OK to delete. 3 isn't big enough to bother with but can be deleted.

 

Yay! Thank you! I thought #1 might be just that, and I'm happy with Windows 10.