They fit a CFL type bulb in them. I would like to replace it with an A19 socket style. Can this be easily adapted or does it need to be rewired?
Those have ballasts in them, so it's not a simple re-wire, per se. Nor do I think any adapter would be available, because of that.
You'd have to swap the guts out (the inner can) with one from a new can, and hopefully it will fit (they're not fun to get back into the can they came out of in the first place, so expect some difficulty).
I don't think you can buy 'can innards'; you'll be buying a whole new can light and just using parts of it.
Another consideration is determining if they're IC can lights (Insulation Contact) and if so, finding the correct replacement 'innards'. But I don't think that's a concern; the 'IC' part of it, is the shell that will remain. I'd just make sure that any replacement had an over-temp cutoff switch.
It sure looks like you could use a common porcelain A19 keyless replacement socket with bracket, like this:
You may find this at a good local hardware store or lighting shop, or order it on the web. You will need to bypass the ballast as mentioned by @Mazura. Alterations of manufactured fixtures void the safety ratings and such (I personally would not be uncomfortable with it if you have good clean wire connections and limit bulb wattage).