Can not update the AWS instance to Rev56

I have my AWS instance and I couldn't import the delivery units because of version mismatch. I have followed this document http://scn.sap.com/docs/DOC-30980, step by step, but when I reached the point to mount the /dev/sdf on the PUTTY.exe, and after I created the directory /sap/update ,I used the instruction: mount /dev/sdf/sap/update

then I get the message:

mount:can't find /dev/sdf in /etc/fstab or /etc/mtab

So what would be the problem.

Regards