Can I tidy up Project Assets.

I have created a video that has over 700 assets. I then Save As to another project which I then delete around 80% of the timeline to produce a video that is essentially an extract of the original. However this still leaves the 700 assets in Project Assets. Is there anyway to remove the assets that are no longer required in the new smaller project? I'm not sure if these "redundant" assets are using space but every time I open the smaller project, it still has to process all 700 assets.