How to change bedtime?

We originally had our son's bedtime at 8:00, but as the son started setting later we changed it to 8:30 because if it were light out when he would wake up after 40 minutes or so he would try to get up as if it were a nap. And yes, we have blackout curtains lol. Anyway, the sun is starting to set earlier again and we'd like to move his bedtime back to 8:00. Should I do just a little earlier every day? And also, will it cause him to wake up earlier in the morning? He sleeps until 8 usually and I would like that to stay. I feel blessed that he sleeps so late but I don't want to lose it. 😅 Any advice or experience?