If you upgrade you Arena 4 licence then you will get 1 new license ( arena 5) and you wont be able to use your old license as well.
Good guess, but wrong.
It all depends on what you start with.
If you own Avenue 4 for 1 computer, you can upgrade to Arena 5 for 1 computer at a discount. Then you can purchase an additional upgrade for Arena 5 from 1 to 3 computers. You do this at the regular volume discount. The total would be €400,- for the version upgrade + €900 for the volume upgrade. You end up with 4 valid licenses: your original Avenue 4 for 1 computer and the new Arena 5 for 3 computers.
If you own Avenue 4 for 3 computers, you can upgrade to Arena 5 for 3 computers for €950,-. The discount is bigger because you already own Avenue 4 for 3 computers. You end up with 6 valid licenses: your original Avenue 4 for 3 computers and your new Arena 5 for 3 computers.
The same logic applies for upgrading Arena 4 to Arena 5.
So basically we're crazy. You get to keep your old versions and pay less for the new ones. And still people complain that it's too expensive.