Since you are using SQL Express, you will need to do this at the service level on some schedule. You will first need to delete the rows out of the table(s) that you want to purge the data from. Something like:
delete BigOleTable where LoggedDate < dateadd(yy,-1,getdate())
that will get rid of stuff older than a year.
Then, you will need to shrink the database.. so, this depends on your recovery model. If you're in full recovery, you'll need to backup the transaction log. and then issue a shrinkdatabase as Tanner alluded to above.