Can I just roll around on the floor laughing. OK done.

Simplest method is to back the site up using Httrack, this will down load a complete copy of your site. Look in the assets folder for all the stuff. 
How do you get rid of old rubbish? 

Gradually by hand - its painful.

We did this for a number sites in Bedfordshire area when replacing e-voice with a more responsive modern solution. www.stondon-pc.gov.uk. Call if you want to know more.