Change material from an array in realtime

Hi,
I’m approching for the first time to Unreal Engine and I saw some tutorials about blueprint, light and materials. I’m working on two projects in which i want to change furniture’s materials (all stored in an array) by pressing a button from keyboard (first) or from two buttons implemented using an interface (second project). I was working on first project for 3 days but i really can’t change materials from the array. If someone could help me it would be awesome!
Thank you community
Lorenzo

Would be great to have more details about your methods, especially code samples where you are assigning materials to array and trying to change ones.

Here my problem. In the 1st image u can see the array; in the other the event graph and the construction script.