To change the licenses you need to be logged into SAP with a Professional License.
Navigate to the License Administration. Administration-->License-->License Administration
Here you can select the the user on the left, and then assign the license on the right. You need to also assign an SAP AddOns, B1i, and SDK tools license to them so that they have full functionality.
In the following screenshot you can see that I have selected our user, nbstest01. On the right section, it shows what licenses are assigned. You can manage license assignments here. It shows a Pro license is assigned to this user. It also shows how many are available.
When you assign a license you also need to assign an SAP AddOns, B1i, and DDK Tools so that you have the full functionality.
Users that are grayed out indicates they are currently logged in. You cannot make changes to their licenses when they are logged in.
When you are done click update / save.