Every time you save your reports a backup of the previous file is made, a backup of that file is also made, and so on - up to 20 generations.
The files are stored in the same folder as your reports (usually in "Documents/ReportPlus/") are saved. The most recent backup copy of your reports will have the extension '.bk0', the oldest available will have the extender '.bk19'. Old '.bk19' files will be deleted as '.bk18's replace them.
Loading a backup file:
Loading a backup file is easy, but should only be done if you think you have lost the original reports file.
Go to "Recovery > Open reports backup > From normal backup". A dialog will appear, select the file you want to load (remember the ".bk0" file is the most recent and ".bk19" is the oldest).
You can turn off the automatic save backups in options:
From within the options window, click the 'Miscellaneous' icon.
You should be able to turn off/on the feature by altering the 'Auto backup' option.