Can I make upgrade to the higher version? How much is cost this upgrade?

Yes, its possible to make upgrade from lower version to the higher versions of the same editions (for example from the Booking Calendar Personal single site usage version to the Booking Calendar Business Small single site usage version).
But its does not possible to make upgrade from the single site usage version to the "developer" or multi site usage versions or from the "developer" to the multi site usage versions.
The cost of upgrade from the lower to higher versions, usually higher than difference in cost between 2 versions.
The cost of upgrade from the lower to higher versions of single site usage versions higher on $5 than difference in cost between 2 versions.
The cost of upgrade from the lower to higher versions of "developer" edition versions higher on $10 than difference in cost between 2 versions.
The cost of upgrade from the lower to higher versions of multi site usage versions higher on $15 than difference in cost between 2 versions.