Help with things

I am a noob. I have started to work on an indie game. And I need help. How do I change the texture of the player in Unreal Editor? When I build, it says something about bounding the lightmass? Those are my rendering issues. For now.

EDIT: Here is the exact error message.

Performance Warning No importance volume found and the scene is so large that the automatically synthesized volume will not yield good results. Please add a tightly bounding lightmass importance volume to optimize your scene’s quality and lighting build times.

You need to place lightmass importance volume and make sure volume bounds are covering your landscape or the level that you have made.