How to overcome the limitation of content database size limit in sharepoint 2010?

Ultimately space is the problem and you need to add more space to the SQL Server. As you are using Express edition, very soon you will face the database size limitation. for more details- http://blogs.msdn.com/b/sqlexpress/archive/2010/04/21/database-size-limit-increased-to-10gb-in-sql-server-2008-r2-express.aspx

Here is another document which highlights the supported features: 
http://technet.microsoft.com/en-us/library/cc645993%28v=sql.120%29.aspx