Before you remove the conrod..... mark or take note of the piston and con rod. It has the half moon cut up at the rear bottom of the piston. The conrod will have the lower 'big end bearing' skuffed at the rear by the back plate and the inner part will be beveled where it goes onto the crankshaft.....important stuff.....
Grap the small "G" clip with long nose pliers. Rotate and pull in towards the middle.
Take both out and replace with new ones. They are cheep and i would never re-use them for a new piston.
While the gudgeon pin is out, give it a good clean and the inside of the con rod.
When you install the new clips, make sure they are in the groove on the inside of the piston.
PS: new piston, are you replacing the ring?