People generally switch to adult food between 6 to 10 months. There's no official age when you should switch to adult food and a couple less or extra months on puppy food definitely won't hurt anything.
What are you feeding now? It is fine to continue feeding the same brand, if that's what you've been happy with, or you an change to another brand if you want. Check out
Dog Food Analysis - Reviews of kibble for a bit of helpful information. Generally, any food 5* or 6* rated is a great choice.