Hey there vandesc!
It sounds like you are having trouble getting your photos to change in the screensaver you've selected on your Mac. We can understand needing a solution for this issue and would like to give you a few helpful tips.
To start, are you using a folder with the specific photos you would like to see when the screensaver is on? If so, when you look at the folder in the Finder, are all the photos showing?
Let's have you change the screensaver you want to use. Do you see all the photos when you use the Photo Wall or Vintage Prints for example?
For steps on how to modify your screensaver settings, look here: Use a screen saver on your Mac
We hope this helps.
Cheers!