It is best not to delete these log files. These are necessary for exchange and also allow you to restore your exchange server from a failure.
There are two legitimate ways to get rid of these logs, and I would recommend the former.
First, Conduct a full backup of your exchange server. This will flush the logs automattically once complete.
Secondly, enable circular logging on your exchange server. Enabling this will no longer allow you to run certain types of backups though, and so therefore is not recommended should you want to be able to restore your exchange server on a granular level in future.
