Use File > Save Numbered Backup to make a backup of your file in the same folder. 

For instance, if your file is called "myfile.sbd", this command will save a copy of the file in "myfile_1.sbd".  The next time you save a backup, it will be called "myfile_2.sbd", etc. 

You can delete older backups whenever you wish, and newer ones will still continue following the highest-numbered backup file that remains in the same folder as your main file.