It depends how you've set up your database. You can set the recovery model to simple to get rid of most of the log file content. Go to the database with SQL Management Studio, right click on the database and select properties. In the popup, select the Options tab and change the recovery model accordingly.
Alternatively, you can do this with a SQL command as well:
ALTER DATABASE YOURDB SET RECOVERY SIMPLE;
If you don't want to fiddle with the recovery model, then you'll need to take a backup to flush the database transaction log.
Afterwards, you may need to shrink the database.
DBCC SHRINKDATABASE (YOURDB, 10);