There needs to be a better UI for levelling up soldiers, the current replacement since the academy was removed I feel is confusing and not very intuitive.
The first image shows a soldier who has not unlocked 4 stars in their Personnel Upgrades. Hence the lock icon over the fourth star. Where Unlock Rank button will take you to the Personnel Upgrades screen for this soldier class.
The rest I think is pretty self-explanatory.
If by ‘Level up’ you mean train (spend bronze orders), then yes that is correct. Training is your progress towards their next star, in your case this would be the fourth star you are training them towards, so you need to have 4 stars unlocked in that soldiers type Personnel Upgrades (Red tree).
