First stop Exchange Server Information Store. Now Start > Programs > Administrative Tools > Services. Right click Microsoft Exchange Information Store > Stop. Leave this screen open.and go to the log directory (drive letter may differ, depending on server setup). Try locating the following directory on Exchange Server hard drive…. “\exchsrvr\MDBDATA.” and log files will be stored here.
Select the files wish to delete and press “Del.” Be careful, not to delete the most-recent log files. It is better to leave all log files created since last backup.
Remember, this ensures that any recent data can be restored if necessary. Quit fro here.
Now restart Exchange Server Information Store. Open the Services screen as leave earlier ! Right-click “Microsoft Exchange Information Store” & press Start & Exit after finish.
Click Start > Programs > Microsoft Exchange > System Manager > Properties > here you can disable circular logs by unchecking the box. For more info is HERE.