Windows

A few days ago I upgraded my Windows 7 to Windows 10 using the direct to pc upgrade. I have a few problems with it and have now downloaded a copy as an .iso file to burn onto a disk. I'm only a tiny bit tech savvy so questions are:

1). Can I reinstall from the iso disk OVER the existing copy or do I have to uninstall everything and then use the disk?

Reasons for wanting to reinstall include (and maybe someone can answer any of these)
2) I cannot right click while on the desktop so I cannot personalise it from there
3) Can i revert back to the older Windows 7 desktop appearance, ie icons and shortcuts on my desktop as opposed to the Tiles on W10 which obliterate my background wallpaper?
4) How do I create a desktop folder that contains all the shortcut icons for linked programs ie Utilities icon that when clicked shows CCleaner, Disk defragger etc etc)
4) How to create desktop shortcuts for things like New Word document etc