I need to change PLG to Hgv, is it easy

Hello There,
I have just bought my self a 4.5 tonn recovery truck.
But I have a problem. It’s been registered wrong .
It’s PLG and as a class 4 mot. Which means it can only carry 600kgs. The Tare weight is 2900kgs
And gross weight is 4.5 tonn. How do I go about getting it correctly sorted.as it as no red class plate to.
Any help would be great . As trying to talk to Vosa is like trying to speak to God.
Thanks Kevin

From my very little knowledge of this I think you need to firstly get in touch with DVLA for the reclassification then DVSA for the new plate

these might be able to help = svtech.co.uk/faq3.html

Many thanks for that Rog