unable to delete snapshots since i have no space in my harddisk

I have recently created a snapshot of but would not like to completely get rid of it because my machine has started to act very strangely since then. However when i choose to delete the snapshot in the Snapshot Manager i was told that i have too little space on my harddisk, but the thing is when i first created the snapshot i was already having very little free space.
Could someone please let me know how i can get rid of the snapshot in my case, please note i have no more space on my harddisk!