The idea of cancelling the upgrades came to mind because some upgrades can be placed on existing belts and some have to place a new tile.
My problem was that I couldn‘t really see my playing field when deciding for the upgrades so I sometimes regretted my choice because of my field constellation :/
Maybe you could add a way for the field to be visible during the upgrading process by making the UI invisible or something?
Or like my initial suggestion make the upgrade cancellable after selecting and realizing that there isn‘t a good spot for the upgrade :)