MS SQL defaults to only truncating the transaction logs once the database and transaction log have been properly backed up. At that point the server will clean truncate and compact the log files.
Obviously, this requires having a backup system in place to backup the SQL databases and trigger that truncation.
If you don't have a backup system in place or it is not backing up, or not properly triggering the truncation process, you can backup/truncate the database by hand using the SQL Server Management Studio.
Backup the Database:
Backup the Transaction Log:
Shrink the Database:
If you run into issues with the transaction log still not truncate, you can use an SQL command to truncate it:
BACKUP LOG <database_name> WITH TRUNCATE_ONLY;
However, MS removed the TRUNCATE_ONLY parameter from Server 2008. In that case, you can use this statement that backs up the database to null, and triggers the truncation:
BACKUP LOG <database_name> TO DISK='NUL:';