Moving Linux image to Windows disk and vice versa, in a dual partition system with two disks

My dual-boot laptop has two SSDs:

1. A 480Gb disk containing the master boot record and Windows. (This disk has lots of free space because I no longer user Windows.)
2. A 180Gb disk containing my Linux install. This disk is pretty much full as I use Linux daily. In fact I cannot install the latest LTS because I don't have enough free space.

I would like to relocate the Windows disk image to the smaller 180Gb disk (currently occupied by the Linux install) and vice versa. Basically, I want to move the OS in the large disk to the small disk and the OS in the small disk to the small disk.

How can I safely perform this operation? I know I will require an external drive, which I am ready to purchase.

Moving isn't really the best way to go about doing this. Instead, you should:

1. Back up all files on both disks
2. Format the 480 Gb disk and install the OS you want
3. Restore the linux files onto the 480 Gb disk.
4. If you want, reinstall Windows onto the other one and restore the files from a backup.