Check your score
Paying off your car loan in full by trading in your car will most likely not help your credit score, but won't hurt it either. Because car loans are installment loans and differ from consumer credit, lenders really only like seeing that you responsibly pay off your loans on time. They don't really care if you pay it off early, lenders like seeing open lines of credit and that you manage them well.
Related: What credit score is needed for car finance in South Africa
Trading in your car to buy another will have a minor impact on your score as you are essentially opening a new line of credit and you will also see a hard credit inquiry on your profile.
The hard inquiry will simply lower your credit score by a few points for up to 6 months. So, from a credit score perspective, you're really not going to help yourself by trading in but it's not like you're going to be majorly affecting your score either.