I believe it’s only selectable when you first create it. The only way I know of to change from Connect to Select is to apply a licence I think.
Personally I’d do the following:
-If you want to try Select then create a new instance (register again) and choose the trial option.
-Keep the Connect instance as is for later use if you don’t want to use Select.
Be aware, there is no way to downgrade from Select to Connect, you can only upgrade.
