How to delete statistics data?

I am running Windows 7 Pro with Unifi 2.4.4. Now everytime i back up my unifi setting, the file getting bigger. After using for almost a year, it is now more than 50MB per back up. I have 21 APs.

How if I only want to backup APs setting and other related settings (without statistics data)? So the backup file will be minimal (maybe a few KBs like the first time we configured it).

Thanks in advance!