Did your Vet tell you to put him/her on Hills? They often recommend it and it's not the best IMO.
What food were you using?
I also have a chubby Lab, last weighed in at 36kg and they also want him down to 30kg. I'd be happy at him being 32kg. He's from showlines and is a chunky boy anyway.
I moved Alfie to Arden Grange Lite from Skinners F&T, but this change was also due to him having a yeast ear.
Many folk don't even change food, just reduce amounts.
I'm sure you'll get more advice on here