Question How would I be able to swap the data between a m.2 drive and a HDD with two different OSs on them?

[tgnd]

Currently I'm using Windows 10 as my main OS on the m.2 drive but I've installed Ubuntu on a secondary HDD and I've decided that I'd like to use it as my main OS with Windows 10 on the HDD if there are any games I'd like to play or programs I'd need to use in the future. How would I go about swapping the data so i could boot from both when I'd like to? I know I could just wipe them and reinstall both OSs but thats not really something I'd like to do.

 

[USAFRet]

Give us a full list of your parts, particularly the drives. Size/make/model...

And then, the current setup - What OS and software is on each.
And then, your desired end state.

 

[popatim]

Do you have a 3rd drive, internal or external?
How big is the M2 and how full is it?
Ditto for the HDD?