Smelly worm bins

I got a worm bin for my birthday about two months ago to compost leftover cooked food that can't go into the regular compost bin. I hate throwing food away but with three kids it's inevitable - and the compost at least makes it more sustainable than landfilling it all. It's a Can O Worms one which was described as 'odourless' and it's even suggested that it can be kept in the house! I have to say mine is far from odourless - it's pretty putrid. Does anyone else have one and what tips do you have for keeping it fresh? I don't put meat into it as we don't eat meat but everything else goes in. It's rat proof so it's not causing those type of problems but I don't think the worms are too happy - they've almost finished with the bottom layer but none of them are moving up to the next layer as they're supposed to do. Each time I move some of them myself they make their way back to the bottom layer, as if they don't like the top layer.

HEEELLLLPPPPP