Exchange 2010 Log files Backup

Hi

I have Win2008 R2 and WinEXchange 2010 server.On D drive is used by exchange log files folder size is 630GB.so I want to take backup of that log files on my external hard drive that size is 500GB.

So I want to know how i can take backup of that log files on external hard drive and clear that log files from the D drive and how to solve the issue related to free space on D drive.

Suggest us the solution on above issue?