So now that I'm getting ready (soon :) ) to fit new pistons in my old Skoda Estelle engine, I found that the piston rods have "wire" C clips. I mean, they look like a piece of wire, no "eyes" or tabs with holes in which we normally put the pliers to squeeze the clip. Just like a C section of a spring. How can be those clips extracted? I guess using a needle-like screwdriver? I have seen this for instance, in power steering pumps, but much larger.
Those gudgeon pin clips are the fiddly type! .. Get a sharp engineers angled scribe or similar, and try to lever one end of the C-clip away from the piston just enough the get a small narrow blade screwdriver under it, use the screwdriver approaching at the same angle as the gudgeon pin goes in. Once you have the screwdriver sat under the clip use the engineers scribe and screwdriver together to work the C-clip out.. WATCH YOUR EYES TOO. sometimes those things come out with rather a lot of force.
Get yourself some retaining ring pliers. You can get them with fixed or interchangeable tips. The interchangeable are cheaper but the fixed tip pliers are better in my opinion. I feel they engage more solidly and predictably than the interchange tip models I've used.
I don't know the situation of your car or cars in general.
But pistons for my scooter come with G- or C-style clips, and have a grove through the bore of the bolt, as shown in the picture below. It's quite easy to grip the clips with needlenose pliers to remove or install them. This works even better if the teeth of the pliers are a little bigger than normal. Ah, and don't grip the clip from the opposed sides, just the wire on one side.