The 5 pushbutton Delco radio presets are set by pulling out the button, tuning in the desired station, and pushing the button back in. You have to pull it slightly to one side as you're pulling it out as I recall. I don't remember if it's to the left or right but I think it's slightly to the left. If they haven't been set up in awhile you may have to get a bit aggressive when you pull them out but they will pull out!
Interesting factiod - every '51 Kaiser Owner's Manual I've seen lists the instructions on how to set the presets but they list it assuming the car has the 6 button GE radio which is a different method! On the 6 button, there is a metal spring tab on the bottom side of each button. You push that spring tab to the opposite side, remove the button, turn the exposed 'tube' counter clockwise till it's loose, tune in the station, then push the 'tube' back in, tighten it and place the button back on it.