File size - additional but deleted items?

users
#1

I have made a large presentation. Then I removed all slides but two.
Though, the file size has not changed at all. I think that the deleted
slides (no, I did not just 'hide' them!) are still there. The reason for my
thought: When I create a 'New' presentation, and import an existing one,
that with only two slides left, all the long deleted slides, after a 'Save'
and a 'Close' are still there. How can I remove a slide for good; and in a
way that it is actually gone; and the file size actually reduced?

Kind regards,

Uwe