(this makes the oldest parts of the log file redundant, the size doesnt change at this point though)
(X above is the size in megabytes that you wish to shrink the size of the log file to)
Assume you had a database called "info" .
To get the appropriate information for this database (e.g. logical file name) load up SQL Enterprise manager.
Right click on the database and go properties > transaction log. The value listed under "filename" is the logical file name of the log file, and the location is the physical location on disk. Suppose for our test database "info" that the value under filename (in the properties > transaction log tab) is "info_log" and location is "C:\Program Files\Microsoft SQL Server\MSSQL\Data\info_log.ldf". Also assume you want to trim the log file to 5 Mb.
With the above information the commands you need to run would be: