How to change location of index files

Hi

I have managed to make search work in our new SP 2013 Enterprise farm. Finally! My farm consist of three servers: two web front ends and one dedicated search server. 

I have two questions now: How do I move the location of the index files from the default location on the C-drive to another drive on the same server (the seacrh server)? And where is the default location?

Thanks,

Jakob