If you have more than 5 qaza Namaaz, then you can pray it any order as long as you pray all the ones you have missed. However there is no sin if they are prayed in the calculated order.
If there is less than 5 Qaza prayers then you MUST pray them in order. E.g. if you missed Maghrib on one day and Asr on the next day then Maghrib prayer of the first day needs to be offered first.
Also, bear in mind that you should not pray Maghrib (for example) if you have missed the Asr prayer before it, until you have not offered the Asr qaza. If you fear that there is a shortage of time for Maghrib and that both cannot be offered in the amount of time then it is better to offer the Maghrib so that you are not sinning by making another Qaza.
hope that helps and good luck!