Delete old events from PowerBroker database on SQL2014Ent

Afternoon guys,

My Beyond Trust PowerBroker database needs a "little" trim. It's currently at almost 650GB size and I'd like to trim the oldest event.
There's a little problem though: I'm not a SQL person and I have absolutely no clue on how to do it. I did try traditional shrink for both files and DB but that didn't change a thing size-wise.

Any chance for some help?

Thanks!!!