If this is your low poly, you have tons of unnecessary edge loops running across the visor, the feet, the waist ... if an edge loop doesn't contribute to the silhouette of the model, delete it.
Thanks for replying. I've managed to get rid of a few unnecessary edge loops, but a lot of them do makeup the robots shape, especially the ones on the visor. I forgot to mirror the arm in the last picture. I've fixed it here. Sorry, what do you mean by this? I plan to keep the white bits in the conecpt drawing solid