1. Click Components>>Akeeba Backups
2. Backup now
3. Backup Now
3. After a successful backup click Manage Backups
4. Find the backup you ran and click the part button. This will start downloading the .jpa file to your computer.
5. If a warning message appears click OK.
Depending on how big your site is Akeeba may break the backup into parts to prevent any timeouts while running the backup. If this happens you must upload all parts: .jpa, .j01, .j02, etc.
If you get an error stating there is not enough memory to save an Akeeba backup you have 2 options:
1. Contact your hosting serice for more server space.
2. Exclude un-necessary files from the Akeeba backup see https://www.akeebabackup.com/documentation/akeeba-backup-documentation/exclude-data-from-backup.html