DBCC ShrinkFile ([log file name]). Check out BOL for the rest.
You normally do not want to shrink the log as it will typically just grow again and the growth process adversely affects performance. What is the recovery model of the database. If you are not doing TX log backups and do not need to restore to a point in time it should be in SIMPLE mode so that the log will wrap. Otherwise you need to schedule log backups to allow the log to wrap and limit file growth.