In Server Management Studio Right click on the database in question and go to Properties:
- Go to “Options” on the left
- Change the line “Recovery Model:” from Full to “Simple” and hit OK
- Right click on the database again, go to Tasks – Shrink – Files
- Under File Type: select Log and click OK
This will temporarily free up space for you, make sure that your database is set to back up and that its configured to empty the log after back up. Once you have resolved the space issue and made sure your log file is set to flush after backups, I recommend you put the recovery model back on Full.