Locate the database that has the ginormous .ldf file, and use either of the following sets of steps to shrink the transaction log file down to a reasonable size: ...

So I have a specific database that won't release and shrink its log files. The DB backups are happening successfully, but I still have 4GB of logfiles (and no, this DB does not generate 4GB of log ...

Then run a backup and that should free the log space, then run a shrink which will reclaim the free space from the database/log files.