Right-click your database in SQL Server Manager, and check the Options page. Switch Recovery Model from
Simple then right-click the database again. Select
Files. Shrink the log file to a proper size (I generally stick to 20-25% of the size of the data files).
Switch back to
Full Recovery Model, and take a full database backup straight away.
You now need to figure out whether you need the ability to recover your database to a point-in-time. If so, schedule regular transaction log and perhaps differential backups according to the requirements of your business.
In case the business can live with a certain amount of data loss, schedule full backups and switch to