How can I shrink the transaction log file (.ldf)

Before this make sure there are free entries by setting the recovery model to simple or backing up the log. 

SSMS
Right click on the database, All tasks, Shrink database, Files, Select log file, 
Click OK

t-sql

dbcc shrinkfile ([db_log_name]) Here [db_log_name] is the logical name of the log file as found from

sp_helpdb or the table sysfiles