Hi there backdrop001,
Just borrow a big external or internal(if you are using a desktop computer) drive from somebody, transfer your data, format your drive and transfer the data back. Keep in mind that you need to reinstall the programs as you can't transfer them as well.
Depending on how much data you have, I guess you can upload it to some cloud storage as well and download it after the format. Though, I would prefer the first option.
Cheers,
D_Know_WD