You can do changes in the cache files and trick cPanel to think there is more space left on the server.
Quote:
You need to edit cache file in /root/.cpanel/datastore,
particularity_bin_df_-P_-k_-l
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Edit that file and change the change of 99% to a lower value, you will then able the use the WHM cpanel features properly.
But it is just a work around so that work will not hamper. You need to remove the unwanted files and need make free space for proper working of the server.