Clearing log files - Exchange 2013

Hi,

looking for a advice regarding logs. My 90GB exchange system drive is getting edged on storage space and I found out there is a 31GB log folder V15 with various sub-folders.

For example, there is ..\Exchange Server\V15\Logging\ContactChangeLogging [4.4GB], full of years old *.LOG files, is it safe to move or delete all of these logs or let's say, all that are month+ older?

Is there any best practice or common tip in general how to handle excessive amount of logs? What's a safe headroom of storage on system drive? Currently i've got 20GB free out of 90GB. Having lesser makes me somewhat uncomfortable.

So far I am taking care just of the IIS logs from inetpub.

All advices appreciated, thanks in advance,

Andrej