Hello and welcome to the communities.
If the built in database maintenance doesn't seem to be doing the trick here's the other way you can do it:
1) Go to Manage > Items in Protect. You can delete your old scan and deployment results from here. If you don't care about keeping any of your old results the easiest way is to choose the Delete All function in each section.
2) You will need SQL Management Studio to perform the next steps. If you have a full version of SQL this should already be available for use, otherwise for SQL express you can download the free management studio express edition from the following links (based on your version of SQL):
For SQL 2008R2 Express: http://www.microsoft.com/download/en/details.aspx?id=22985
3) In SQL Management Studio, do the following:
-Right click the Protect database and go to Properties. Then go to the Options. Set the Recovery model to Simple rather than Full. This will help keep the size of your database log file from growing too large and allow it to shrink as well.
-Run a Shrink on the database. Right click the Protect database, then go to Tasks > Shrink > Database. Hit 'OK' on the next screen to run the shrink.
I hope this is helpful. I've also attached a full guide on Protect database maintenance.
THANK YOU!!! That shrunk my db from 6.2 Gb to 500Kb! Problem solved.