Swapping IMacs (24in,early 2008/27in, late 2013)

My friend and I are swapping IMacs. I have an older model (10.10.5; 24inch, early 2008) Processor: 2.8 GHz Intel Core 2Duo; Memory 2 GB 800 MHz DDR2 SDRAM; 640GB HD. My friend has (10.10.5; 27inch, late 2013) Processor: 3.4 GHz Intel Core i5; Memory: 16GB 1600 MHz DDR3; 1.12 TB Fusion Drive.

What is the best way for us to switch computers and the date we have on our computers?