How to change the center of a mesh?

As the following image, I use the TriPyramid mesh, but the mesh is now rotating along its bottom not the center. How can I make it rotate along its center?

I think there’s something wrong with that picture of yours… it’s not there. Since you don’t provide much information, I’m gonna assume that you have an actor with a mesh component and when you rotate it, you’re not happy with the center of rotation. If that’s the case, the easiest way is to use a scene-component as root of the actor and parent of the mesh-component. Then you can move around the mesh-component relative to its scene-component parent, which becomes the center of rotation.