Adding a SSD on existing configuration

Adding a SSD on existing configuration

I want to install a SSD to speed up my computer, but I'am still unsure on
how to.
I currently have 2 hard drives of each 500GB partitionned into one volume
of 200GB for the OS and software, the remainder for data storage. These
hard drives use the only 2 SATA3 connections, there are also 4 SATA2 ports
which are currently not used.
So when I install the SSD, do I just plug it in a SATA2 port? Or should I
transfer one hard drive (or both) to the SATA2 port so that the SSD can
use the SATA3?
Thanks!