There are a couple videos on youtube showing how to install a ssd that connects to the SATA_3 header on the motherboard. The SSD area and DVD is a caddy that is easily removable if you take out the cpu fans and heat sink. If you don't want to do that then you have to go the way of disassembling the front of the case a bit to slide the SSD into place.
I much more liked removing the CPU fan and heat sink--I had to repaste and add ram anyway. Doing it this way made it really easy to install the SSD and secure it with a couple screws. It is also a lot easier to make the cable connections in my opinion, plus you would have to remove the caddy if you still need to connect a cable to the SATA_3 header.
If you do secure the drive with screws, they have to be flat head. I used some old screws that had more of a pan head and they interfered with properly re-seating the CPU fan assembly.
https://www.youtube.com/watch?v=k7NroUI3UPYhttps://www.youtube.com/watch?v=7T_4eRNoHNk