We did it gradually! We started by putting his junior bed in our room so he knew we were not going anywhere ( might not be possible in some rooms even ours was a tight squeeze )

Then once he was sleeping all night we just moved his bed and made a big deal about it that its a big boy bed etc

I personally think dont try to rush the transistion, and if it means a few more sleepless nights to do it calmly and so your child feels safe then its worth it!

It will happen good luck xx