Follow the instructions below. If anything is unclear please ask first.
- Open compmgmt.msc
- Navigate on the left side to Disk Management
- Right-click the recovery / system partition and select change drive letters and paths
- Map a drive letter
- Open windows explorer to browse that drive
- Delete unneeded files to free up space.
- Remove the drive letter by using compmgmt.msc again.
- Reboot the machine.