Hey, the ways for you to resolve this low disk space problem could be different according to your different conditions:
* If there is too unnecessary files or programs stored on this C partition, clean them all up to free some free space.
* If there is enough free space on other partition, like D, E or F partitions, you can open Disk Management, delete or shrink the partition with free space and add the free space to your C partition there.
* If the free space is not adjacent to your C partition, you also can use a partition resizing tool to extend this partition, like GParted, IM-Magic Partition Resizer Free and Active Partition Master, etc.
* But, if there is no any free space left on the same physical drive, just buy a larger one to replace the old one.
No matter what your conditions are, just save all partition data on other places in case of data loss.