It means that you have 75 GB used on your c-drive and 257 GB used on your backup computer. Probably a lot of old files, or the overwrite doesn't work. Or you backup too much (such a all temporary Internet files).
The settings probably are in the backup program you run. Please tell what program. I don't think it's native Windows functionality. So if you don't know, ask the person who set it up for you.
And better cleanup the c drive. It is too full.
I have a remote HD attached to my computer. It was set to auto update and overwrite existing data. However my C drive shows 4.79 GB free of 79.9 but my remote HD says 41.6 free of 298 GB. I am not particularly computer literate and would like to know how to check the settings. Many thanks.

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