Dell G3 15 (3579) Low disk space on C drive

I have owned a Dell G3 15 (3579) for less than a year and am already running out of disk space on the C drive. The system is telling me that I only have 119GB of storage on this drive. When I purchased the computer I was told that it has 1TB of storage but I can't seem to find where this amount of storage is. Can someone please help as I am hopeless with any form of technology!