Your understanding is mostly correct – the bottom number does indeed show the budgeted amount of the Envelope. However, the top number does not show the amount left for the current month or period so much as it shows the current balance of that Envelope. Oftentimes, particularly if you reset your Envelopes’ balances to the full budgeted amounts each month, that number does indeed show your spend for the month, but that is not always the case.
For example, consider your Eating Out Envelope – if you Filled it to 100 one month instead of the full 400, the top number would read 100 rather than 400, even if you hadn’t spent anything yet that month.
I hope that makes sense, but you can see another elaboration in our Help Center here in case that might be helpful.
As for whether you can change what numbers show up next to the Envelopes, this is not possible. The top number will always be the current balance and the bottom will always be the budgeted amount.
Hope that helps!