First backup your transaction logging:

  1. Tasks > Backup
  2. Select transactionlog backup en select a disk where to backup
  3. Now check the status with DBCC LOGINFO(DATABASENAME)
  4. Check if the last status record is 0 (zero)
  5. When the status is 2 make another backup
  6. When the status is 0 you can run: DBCC SHRINKFILE(2)

You can use this script also: Backup LOG DBNAME TO DISK = 'C:\SQL_TMP\transactionlog.trn' WITH STATS GO DBCC LOGINFO(DBNAME) DBCC SHRINKFILE(2)