Hi phillpower2! I am not too computer literate, but I will try to give my best explanation. After performing this operation, I would recommend a modular psu as there was very little space in my computer. It is a good thing that I have slender hands, and a very good helper (my 14 year old son), or I don't think I could have done this.
My new purchases: PSU CORSAIR/CMPSU-650TX 650W RT and VGA ASUS ENGTS450 DC OC/DI/1GD5 R graphics card
After I removed the computer cover, I evicted all the dust bunnies I found living in my computer. Then I removed my old graphics card. I did this by swinging open the card retention mechanism (one release tab), then swinging open the card retention door by pushing on the two release tabs. There was a securing tab on the card that I pressed and out came the old card. The new card was much bigger than the old one, so I removed an extra card panel insert. Also, I had to remove the card retention mechanism as it would not work with the new graphics card. I inserted the new graphics card, making sure it was seated properly and secured, and shut the card retention door.
I had no trouble removing most of the old psu cables, however, I did have a cable that went all the way to the bottom at the back of the case, for my hard drive. To get at this cable, I had to remove (tilt back) the heat sink assembly (took out two screws). Then I used a flat head screwdriver to pop open the two square plastic clips that held this cable to the case. After feeding this cable through a metal part of the case, it was free. I removed the screws to the psu. I had to press on a clip at the back of the case and out came the old psu!
After studying all the cables on the new psu, I came to the conclusion that I would not be able to hook up the cable to my hard drive the same way as the old psu. I replaced the heat sink cover. I placed the new psu in my computer and quickly discovered that it was longer than my old psu, and it left very little space get my hands in to hook up my cd and dvd drives. This is where I enlisted the help of my 14 year old son. He held the new psu just outside the case, while I hooked up all the cables I needed, including the new graphics card. The cable to my hard drive was fed above and around the heat sink (there were a few cable slots there). When everything was hooked up, I placed the new psu into the computer and screwed it in. I noticed that the back computer cover frame overlapped the raised area where you plug in the psu and the frame stuck out a wee bit. It did not interfere with the computer cover nor hinder my plugging it in, so I left it as is. With patience (alot of cursing & apologizing to my son), and determination (high spike in blood pressure) I was able to fold the excess cables in to the space between my cd/dvd drives and the back of the new psu, so that the area underneath the psu was clear to allow air flow, and none of the cables became unhooked. To be honest, the cables look like a pile of snakes, lol--hisssssssss.
All of this took me just over two hours to do ( with many little breaks). I am assuming that I did this right as my computer is working wonderfully, especially when watching movies. I would like to mention that there is a half inch gap in the case at the bottom of my new psu at the back of my computer because of the difference in sizes. Should I cover this up or leave it be?