Vias: select a via you want to change, right-click -> find similar objects, then set "hole size" or via diameter to "same" and click OK. It will select all vias of that size/diameter and bring up the PCB Inspector. In the PCB Inspector, change the Via Diameter and Hole Size, and it will change it for all selected vias.
I think you can do the same thing with pads, but I wouldn't do it because the footprint will no longer match the library. Better to edit the footprint in the library; I normally create a PCB library for the board (Design -> Make PCB Library), then I can edit a single library instance of a footprint, and update the entire board with it.
In the PCB Library editor, you select the footprint you want to edit, then select the similar pads you want to change, either the same way as above, or you can multi-select in the Component Primitives window. in the PCB Inspector (View -> Workspace Panels -> PCB -> PCB Inspector) change the Hole Size and Top & Bottom Shape & Sizes. If you increased the hole size, review the internal layer clearances to see if they need to be changed. Then right-click on the footprint name in the Components list and "Update PCB with..."