Trimming your database is a sensitive issue b/c it can result in data loss that you don't want. I recommend contacting support so they can walk you through it. To do so, open a support ticket here.
Click Submit a Technical Support Ticket
In order to receive technical support, you will need to be current on your SolarWinds maintenance. Complete the form. You will not be able to upload your diagnostics, but you will receive an email back that allows you to upload diagnostics.