Not disagreeing with ROG, but you could upgrade your car to manual simply by taking another test. You will then “automatically” gain manual entitlements on your vocational licences.
There’s nothing wrong at all with trying to upgrade on a manual truck, provided you can find one that behaves itself. Most manuals will be operated by those folks who cant afford/be bothered to change to auto. The rules changed nearly 5 years ago so no reason not to have changed IMO. So, if you’re considering using a manual truck, I strongly suggest you have a trial lesson.
People who have driven trucks with well worn manuals will know exactly what I mean.
Pete 