how to clean the charcoal grout, help please - Tile Advice

[igor]

Hello

Does anybody know how to clean the charcoal grout from the porcelain tiles?
Someone told me the that there are some LTP cleaning liquid that is good for that.
I googled it and there are a few different ones. Which one should I go for?

Thanks

Here are BEFORE and AFTER photos:

 

[Andy Allen]

what tiles are they ..

 

[igor]

it's porcelain tiles