UV Channels in the Static Mesh Editor
In the Static Mesh Editor UI, you can list, visualize, and remove UV Channels.
Listing UV Channels
When you have any Static Mesh Asset open in the Static Mesh Editor, you can use the UV button in the Toolbar to list all the UV Channels in use by the current Static Mesh.
Visualizing a UV Channel
Select any UV Channel in the list to visualize the mapping of the mesh's triangles into 2D texture space as an overlay in the Viewport:
Select None at the top of the list to hide the UV overlay.
Removing a UV Channel
When you have a channel selected in the list, you can remove it. Each UV Channel stores texture coordinates for each vertex as part of the Static Mesh, so you may be able to save some runtime memory by removing any mappings you don't use.
All other UV Channels that were present in the list after the deleted channel are moved up one spot, to fill the empty space left by the removed channel.
You can't delete a UV Channel if your Static Mesh Asset is set up to generate lightmap UVs, and the UV Channel you have selected is already in use as the source or destination channel for lightmap UVs. Either deactivate the Build Settings > Generate Lightmap UVs option, or change the Build Settings > Source Lightmap Index and Build Settings > Destination Lightmap Index settings to point to different UV Channels.