Depending on the specific situation, there could be several solutions.

If the part you want to delete is a separate object, you can just select it and delete it.

If the part you want to delete is a separate material, you can make it 100% transparent. This doesn't delete it but you won't see it in the render.

If neither of the above is true, a possible solution would be to create a transparency map where the parts you don't want are white (transparent) and all rest is black (opaque). To create the transparency map you could export the texture map, convert it in a 2D image editor in a black and white image, and do as I described.