Remote conversion of 32-bit CentOS 6.3 to 64-bit Ubuntu 13.10
Pretty much any Linux should be fine as long as you have suitable scratch partition for temp Ubuntu install, in this example we're re-using 6GB swap partition. Process is two step, first we do minimal 32-bit Ubuntu install over swap partition, boot system, hack it to 64-bit and finally do final 64-bit Ubuntu install over old CentOS rootfs.