I had to chime in here as I was able to do this fairly easily a few months ago and I am NOT a hardware techie at all! After doing this successfully once, I went ahead and replaced about 4 SATA drives with SSD!!
You buy a samsung SSD: 1 TB should do. It comes with Samsung migration software to clone your existing HD. I actually used another freeware available online called Macrium reflect to clone the existing hard-drive (you connect the new SSD by USB and clone it). There are excellent youtube videos on using macrium. For one HD, Macrium kept getting stuck and I used the Samsung migration for that one, successfully. You will only run into problems if the new HD is SMALLER in capacity than the old one.
Once the disk is cloned, you open up the tower and put it in place of the old HD and your computer will start up and everything will be back to normal except it will be faster! I had difficulty getting one SSD to fit into the 'roomy' hard drive bay: I just taped it in with electrical tape!
