First of all, Shrinking is bad. Shrinking log file on regular basis can cause issue in the fragmentation. You can simply shrink your transaction log file by following simple steps in http://www.sqlserverlogexplorer.com/how-to-clear-transaction-with-dbcc-shrinkfile/

If you have taken log backup, then run DBCCLOGINFO command and look entries with Status=2. Status 2 indicates the portion of log is active. If your active portion of logs is at or near the end of log file, then this will prevent the log from being shrunk.You need to setup and run frequent transaction log backups.From this the active portion will again be at the beginning and you will be able to take shrink your file!