How to Backup my iphone to an External Harddrive?

I use itune to backup my iphone. But my computer's C drive doesn't have enough free space to backup my iphone. Can I backup my iphone to an External harddrive? My computer's operating system is Windows 10.

Also, how can I know the location of my previous iphone backups in my computer's C drive? I need to delete some previous iphone backups.