Sorry, but Minehut does not allow any servers to change versions, Minehut will update when all plugins are updated to the newest version! But, if you want 1.8-1.16 to join your Minehut server, install the ViaTrio, which is what I like to call it, it is these three plugins: ViaVersion, ViaBackwards aswell as ViaRewind. If you just want 1.9+ you only need to install ViaVersion and ViaBackwards.