If you can live without the documents all together then you will find a purge facility for documents older than a certain date in the Maximizer Administrator programme. Please use with care and back-up your database first as once purged documents are not easily restored.
If you are reaching the 4gb limit you do have the option with Maximizer 11 of upgrading the SQL express to 2008 R2 which will increase maximum storage to 10gb.