I found it really helped to let our Syrian play in the cage a couple of times before moving him over. He had a very bad move the first time I upgraded him (I put him in the new cage cold turkey and he was very strange and shaky for about 10 days). So the next upgrade I filled the base with Fitch, put a couple of toys in and let him go in for a play. He was interested for a little bit then panicked and wanted to come out again so I popped him back in his old cage and he dived into his house. Then a few minutes later he came out again and sat at the door wanting to come out as if to say - I think I'd like another look! So I put him back in the new one again and this time he was in there for ages and explored every little bit of it! And enjoyed it. I left him till he was ready to come out again. I then left it a day and the day after, put him in his pet carrier up in the bedroom for a couple of hours while I moved everything over from the old cage to the new cage and got it all set up and ready. He settled in straight away.
It was a bit tricky having two blooming cages in the room for 2 or 3 days but the other members of my family tolerated me leaving the Barney on the table and eating of their knees for those 2 or 3 days
As Crayola Laura says, when you move him over, keep all his old substrate and spread it out on top of the new in the Barney cage. There won't be that much substrate from the smaller cage so fill the base of the Barney as deep as you can and spread the old on top of that so it smells familiar. The good thing about the 7mm bar spacing on the Barney is the substrate doesn't fall out through the bars
I've had it piled a few inches up the bars in places and it doesn't fall out, so don't let that stop you filling the base to the top. It does take quite a lot of substrate, but that will last a long time.
Also try and put his familiar toys etc in a similar layout if you can and don't clean anything before moving things over. They'll be fine for a couple of weeks. I scattered some food around as well as that distracts them from feeling strange as they roam around pouching it. Try and save all his nest and pop it in the house. And have a huge pile of torn up strips of plain white toilet paper somewhere in the cage not far from the house so he can pouch it and rebuild his nest. I wouldn't bother moving any of his hoard over but maybe put a bit of new food inside the house as well as scattering and having a food bowl.
Then it's the same as when you first get them - leave him alone to settle in for 2 or 3 days. Unless he shows he wants to come out and play! And try not to disturb or clean anything for the first two weeks. Although adding the odd new thing is usually fine as long as you don't move things around while he's still scent marking so he can find his way around.
It's quite open in the middle so if you have a tube or tunnel or cardboard box to put in the middle of the cage that breaks up the open space