How do I reduce MySQL usage?

[California_Dreamin]

I've been informed by the Terms of Service Compliance Department that I need to reduce my account's MySQL usage to a maximum of 3GB. This what they told me:

Your account information:
Total MySQL Database Size: 5193.26 MB
Total MySQL Tables: 664

Largest MySQL Database Size: 802.69 MB
Largest MySQL Table Count: 35

"Take a look at the mysql usage tool in the databases section of your cpanel. Take a look at the size of your databases and which tables are the biggest. Those tables are the ones that need to be reduced. The total size of all of your databases is currently 5274.76 MB. We will need you to reduce that to 3GB or less. Let us know when you are ready for a rescan. Thank you."

Problem is, though I took a look at my database tables, I don't really understand them.
Right now I have 19 WordPress sites (one primary and 18 addons) installed plus one subdomain.

My question is, Do I have to reduce the number of addons I have or can I reduce my usage by cleaning up my databases?

As I'm sure you can guess by my question, I'm way over my head technically here, so please type slowly when replying.

[REXTEX]

If you have tables which collects info from your users, you may need to delete the older data from these tables. For instants I have a refer table that loads up with alot of data on a daily base's, so in my PHP script I have it dump the data which is older then Five days.

[alemcherry]

You need someone technical to look into your database and see if you can reduce the size by deleting some unwanted data like logs etc. Probably this is easy and can be done by disabling some plugins, changing some WP settings etc. Hard to give a solution without seeing the data / files.

Ofcourse, you have the option to get another account and move some of the add-on domains to that. 6GB of databse on a $8/month shared hosting seems like frankly speaking- abusing the resources.