SQL 2005 Standard Edition - msdbdata.mdf size

Hi,

I have sql 2005 standard edition and notice that the system DB is very large (msdbdata.mdf). It's 3.8GB in size. How can I find out what is it in and how can I clean up the DB and remove the stuff that is not needed? I don't have much knowledge in SQL.

This is the SQL DB:

sql 2005 standard edition -> microsoft sql server management studio -> databases -> system databases -> msdb (msdbdata.mdf) -> 3.8GB in size

I'm planning to move from sql 2005 standard edition to sql 2008 r2 express edition. Does the 10GB limit apply to the system DB for sql 2008 r2 express edition as well or only non system databases?

Thanks!