Cleaning new porcelain tiles

Hi Folks. We're moving into our new house soon (bring on the debt!!) but before that we have to clean the new tiles put down before the kitchen units went in. They have boot marks etc on them and was wondering what would be the best substance to remove these stains without damaging the tiles.

We have marble in our hall and found Lithofin products the best. They have lots of product information for porcelain on their site. You can get their products in most tiling stores. Not cheap but a good product.
I have no affiliation with the company.
http://www.lithofin-uk.co.uk/product_template_KF-FZ.html

Thanks Ann1