Depends what linux resources you have, in that this will do it, but you need to have the filesystem not doing anything, so at the least stop the media center (it would be better to do it on a separate system, not the OSMC):
[code] Once booted:
sudo fdisk /dev/mmcblk0
Delete the second partition (d, 2),
then re-create it using the defaults (n, p, 2, enter, enter),
then write and exit (w).
Reboot the system, then:
sudo resize2fs /dev/mmcblk0p2[/code]
I’m sure a better source will comment if this is a bad idea!
You need to identify the disk name for the SD card, and you’ll need to check you have the fdisk and resize2fs available
Derek