STEP 1
Head to the directory where the bank file is stored
Windows location
Spoiler : Path :
Mac location
Spoiler : Path :
STEP 2
Copy the "Mbank13.SC2BANK" file into wherever you think would be safe or convenient for you, such as;
- Cloud Storage services (Dropbox, Google Drive, Microsoft OneDrive, Apple iCloud, etc)
- A flash drive/External HDD
- Another computer/laptop
Pro-Tip
You can use software such as "Everyday Auto Backup"(suggested by Sureiya) to automatically copy the banks file/folder at set intervals of time to another location.
To Restore your Bank
Put the "Mbank13.SC2BANK" data back into your StarCraft II installation, go to the same directory from step 1 and replace the "Mbank13.SC2BANK" there with your backup copy.
This guide was written by @Mugy I just gave it its own thread.