Dandruff and How to treat it correctly?

I’m 13, and have realised that I’m getting a small amount of dandruff. It’s no itchy or anything just looks a bit unpleasant. I’ve been using anti dandruff shampoo over the past few weeks (once a week) but have found it’s making no difference and is coming in worse the more I use it.

What could I do to get rid of it?

Thank you.