New
#21
You made some valid points. Since you are inexperienced with working on computers (nothing to be ashamed of, we all were there once), the easiest route would be a variation of what our friendly, neighbor bear suggested.
Get a second external drive and copy all your data to it (also make sure your backup drive is up to date), then delete the data from the computer before taking it into the shop. Ask the shop if they can install a second HDD in your computer (if not, ask them to make a separate data partition on the one drive).
When you get the computer back, copy your data onto the new drive (or the old drive if the shop couldn't install a second drive). Keep one of the external drives at home for your onsite backup. Keep the second external drive somewhere offsite, such as at a trusted friend's or relative's home, in a locked locker or desk drawer at school or work, or in a safe deposit box at a financial institution. Swap out the two drives as often as possible to keep the offsite backup as up to date as possible.