I am going to reinstall Windows on my computer so that I can flash the BIOS (the computer manufacturer only supplies a .exe file). I would like to efficiently reinstall Ubuntu after that. Can you explain a time efficient way to do that?
The most efficient way is to find a Live Windows image and boot from it.
You will be able to flash BIOS from it.
But beware that in some cases it is not a good idea to flash a new BIOS. About a week ago I flashed a new BIOS to an Asus laptop using a BIOS utility (built in into BIOS called EasyFlash).
After that I lost touchpad in Ubuntu and had other problems. I couldn't downgrade BIOS using the same utility because it didn't allow to flash older BIOS.
So I had to use a Live Windows image where I successfuly downgraded BIOS using
So if you don't have a very strong reason, and everything works fine, don't upgrade BIOS. Ubuntu will take care of CPU microcode.
The most time efficient method of putting an existing Ubuntu installation back on your system is to boot from a thumb drive, do a complete image backup of the entire drive to another (large enough) storage device, then restore that image backup after you're done with Windows.
I'll link an article on how to do this (be careful; you can erase everything as easily as backing it up), but
dd is the core command for these operations.