Orthodontic treatment can be carried out on one jaw only, if the case allows it. In some situations it is possible to correct just the six front teeth without involving the rest.
Partial treatment of the upper or lower jaw is possible if the teeth in the opposite jaw do not prevent the desired movement. Partial corrections like this are usually done in preparation for later restorations, such as veneers or bonding.
In every case, a detailed orthodontic examination is needed to determine whether this kind of treatment is suitable.
This answer is for general information. Your own case needs an examination by an orthodontist.