First, A bulletin board is not the first place you should turn to ask legal questions. Go here:
Graduating from a Junior to a Senior License
Junior Driver's License may be changed to a regular, Non-Commercial Driver's License when you meet the following requirements:
Held a Junior Driver's License for 1 year,
Have not been convicted of any violation of the Vehicle Code,
Have not been in an accident for which you are partially or fully responsible.
Has successfully completed a driver’s training course approved by the Department
NOTE: A Junior Driver's License shall automatically become a Regular Driver's License when you turn 18 years old.
The key is the last sentence. You don't do anything, once you turn 18, your junior license is a senior license but will say junior until you need it renewed and get a new one. There is no curfew once you are 18.
I have three kids. The older ones are 22 and 20 so I have been through this with them. Drive carefully!