He probably means the top part of the boots are too lowpoly, specially edges of the cloth. This could be fixed by increasing geometry or applying tessellation shader how @Axi5 mentioned. But for me it looks ok. Another trick is to change topology of your geometry and increase vertices where it is necessary.
@Axi5 wow man why didn't i know that. So lets say i want to make a CAVE with really nice background cave walls. I already make the cool procedural textures in substance designer. Then what i need to do is just make a deformed plane following the outline of the cave, and apply that material in marmoset?