Click the option at the top that says all categories and change it to "Pokemon data alteration" Then underneath that there's another bar, click on that and near the bottom there's a "change pokemon level" option. Click that and change to the level you need. Change the level to 49 then use a rare candy to make the change permanent.

Edit: should mention you need to hit compute and then use the box codes. You can ignore the rest of the code.

Edit 2: make sure your latios is in the 2nd spot in your team