iMac 27" Late 2012 HDD replacement to SSD

Hello,

I have iMac 27" Late 2012 MD095LL/A A1419 (EMC . It has 1TB HDD. I want to open it up to replace the HDD. I have another Macbook Pro Late 2006 2.33 GHz 2GB RAM and replaced its HDD with SSD and it's running much faster than my 2012 iMac 27" with 8GB RAM, but 1TB HDD.

So I want to ask two questions:

1) Can I do it in a way that I leave my current 1TB HDD inside and add another 256GB SSD, so I can have both together? I mean are there the required connectors / space inside?

2) If above not possible, then I will just replace 1TB HDD with 256GB SSD. Would I require to purchase some special dock for SSD to place it properly?

Thank you very much in advance.