Highlighted tags on our job ads are determined using an algorithm that takes into account what tags you most frequently visit on Stack Overflow and therefore what we think you're most likely to be interested in. You can read more about this in our blog post here.
You can see what data we hold for you by visiting the prediction data download page.
We are aiming to make this more customisable in future - perhaps by taking into account your liked/disliked tags in your Careers profile and favourite tags in your SO profile. However, at the moment, there's little you can do to directly change how the highlighting functions.
It's worth noting that all the jobs you see in the ads are accessible using our job search functionality and you can configure alerts to get jobs of interest to you sent by email.