Root partition is filling up - UTM 9.7

Hello, 

our SG 125 rev.1 is still sending email:

Root partition is filling up - please check. Current usage: 93%

--

HA Status          : HA SLAVE (node id: 1)

System Uptime      : 0 days 1 hour 6 minutes

System Load        : 0.10

System Version     : Sophos UTM 9.705-3

 

Please refer to the manual for detailed instructions.

I tried to use this tutorial www.youtube.com/watch but in thsi folder are not big files. Can you help me what I should do please? I am not so experienced with linux.