You do not have an option of how the adverts are placed.
It's probably best to search the forum for recent posts including the terms "ads" or "adverts" to get an idea of where they appear. Make sure you only look at the most recent posts as things have been changing. I get the impression it's a slightly movable feast at the moment as Nabble tries to find a way that brings most revenue for them while trying to find somewhere with the minimum impact for users - a near impossible task that's always going to leave longer serving administrators, used to an advert-free forum, aggrieved!
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.