Managing Transaction Log Size using a Maintenance Plan
If your log file is growing that large then you are doing at least one of these things wrong:


if you need point-in-time recovery, then you are not backing up the log frequently enough (and perhaps the database too). Perhaps you have created a maintenance plan to back up the database daily or weekly, but haven't configured a maintenance plan that backs up the log.
if you don't need point-in-time recovery, then you are in full recovery model but shouldn't be. You should be able to switch the recovery model for your database(s) to simple. This will mean that you will only be able to recover to the time of the last full or differential backup, but it also means your log file will stay in check on its own.
in either recovery model, the problem may be that you have an extremely long-running transaction. As in, someone called BEGIN TRANSACTION, locked their workstation, and went on vacation.


A lot more details about this can be seen in this question:


Why Does the Transaction Log Keep Growing or Run Out of Space?


In order to shrink the log for now, if you are in full recovery model and want to stay that way, you should perform these steps and restart your log chain to be safe:

USE [master];
GO
ALTER DATABASE db_name SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
GO
-- if you are already in simple, remove this line:
ALTER DATABASE db_name SET RECOVERY SIMPLE;
GO
CHECKPOINT;
GO
-- if you're already in simple, or want to stay that way, remove this line:
ALTER DATABASE db_name SET RECOVERY FULL;
GO
BACKUP DATABASE db_name TO DISK = 'path' WITH INIT, COMPRESSION;
GO
USE db_name;
GO
DBCC SHRINKFILE(N'db_name_log', 30); -- pick some size that makes sense
GO
USE [master];
GO
-- if recovery is full, re-init log chain, otherwise remove this line:
BACKUP LOG db_name TO DISK = 'path' WITH INIT, COMPRESSION;
GO
ALTER DATABASE db_name SET MULTI_USER;
GO


I commented lines that should be removed if you're already in simple (highly unlikely) or if you want to switch to simple.