All of that information is stored in your /home/osmc/.kodi folder and therefore taking space up on your SD Card. 2GB is really at the edge for any productive system. Recommend at least 8GB card.
While you could move the stuff on an external HDD (or do a USB install) but I would recommend to just take a bigger card.
I ran into the same problem a couple days ago. I ended up moving my ~/.kodi/userdata/Thumbnails directory to my external usb drive and making a symlink to it.
osmc@osmc:~/.kodi/userdata$ ls -al Thumbnails
lrwxrwxrwx 1 osmc osmc 43 Oct 23 12:31 Thumbnails -> /mnt/Main/Backups/.kodi/userdata/Thumbnails