Download CPU-Z. It's a small program that will tell you what you need. Everest Home Edition is also very nice but it's a bit larger download.
The Download link is in that page in the top left corner (CPU-Z 1.36). You don't need to install the program, just unzip the files in any folder in your computer. Afterwards, run it. You'll get a screen like this:
I have highlighted in yellow what you're looking for: the type of socket your CPU is mounted in ("Package"). In my case it's called "Socket A" (fairly old; i'm upgrading soon.) Hope that helps.
Edit: seems I have an older version of CPU-Z, getting new one
... There, updated to 1.36, and updated screenshot.