I think i know (or guess) what the problem is.
You open your widget and do blueprint code inside of it. There from inside of widget you can change image_25.
Do not do code changing stuff inside widgets in other places. Well not directly, use blueprint communication methods.
You can make HUD widget, (or player pawn or player controller will do). Then it that hud widget you make dispatcher that sends data needed (like HP, mana etc) then widgets hook to dispatchers and read/update that stuff.
For changing image etc, you code that thing inside widget (like creating texture reference variable and exposing it), then you add some code that replaces texture inside widget.
Well best would be if you followed some tutorials, my rambling here about all communication with widgets is not optimal to learn from. 