I'm sorry if the question has been already asked, I couldn't find it.
I bought a raspberry pi 3 2 years ago, and I still use it with no problem. I bought a new rasp pi 3 b+ 1 week ago, and I tried to use the same image in my other SD card but I stucked on the rainbow screen. After some research, I found that the problem lied in the raspbian version. So I tried with a new raspbian and had no problem to run it.
Now I'd like to know if there is a way to update my previous image so it can run on my new rasp?
Thanks in advance