I Extruded up with z and scaled down 8 times but have a square to deal with You're looking at a leather seat from a dining chair. I modeled this chair seat by creating the very bottom loop of vertices then extruded them up and scaled down many times using the image planes as a guide. I was surprised it worked as well as it did but in the picture you can see what I ended up with at the top.
Maybe there's a better way to model this?
Thank you for your help!!
If you want the center to be just vertices (As shown in @Neil's answer), click alt+m while only selecting the square in the center.
But if you want the center to be a circle:

Select only the center square
Press Space bar (EDIT: Press F3 instead as Space bar was for an outdated version of Blender)
Type in sphere and click the to sphere option.
mess with the values in the tool bar (Scroll to bottom of toolbar) to get your desired result.