Free space from image column after update
Removing data will not release the space used by to the filesystem unless you then perform a database (or per file) shrink. The newly unallocated space will get used by new data as it comes in before any more is claimed from the OS by growing the relevant files.

If you need to fully reclaim the space then you need to look at DBCC SHRINKDATABASE and DBCC SHRINKFILE, though don't do this unless you have to as it can cause internal fragmentation that if allowed to build up can impact performance.

When you take a backup only used pages are included, so you will see backup sizes drop even though the actual database size has not reduced.