Cream tiles grout gone brown

[OnTheNiceishList]

I have lovely cream tiles in my house but the grout has gone dirty and brown over the years. I did spray seal it to keep it clean but that’s not worked. Hopefully it first stop me cleaning it.

How can I bring up the grout to a nice clean white?

If it has been years I'd get it regrouted.

You can try the top up pens, but IME it's best just to get the job redone properly and avoid the faff.