Reason for using roll pins instead of solid pins is they provide a mechanical lock of the pin so it won't slide out of holes or parts it's locating. Correct size would be a hair larger OD than the hole it fits in, so that the pin walls are forced to compress slightly. That compression pressure keeps them locked in place.
There's some handy punches that can be real helpful for knocking out roll pins without damaging surrounding metal or having punch slip: Transfer Punches.
At the link the picture pretty much tells it all, but they come in all different sizes according to diameter of hole, or in this case diameter of roll pin. That nib on the end centers itself in roll pin's hole so it doesn't slip when driving out pins. Choose one the same OD as roll pin.
I don't like to shop Harbor Freight for ideological reasons, but their picture was good: