Resin grout

[cully]

I have a steam room that I grouted with apoxy resin about 15 years ago and the grout is becoming dull in places, showing signs of age.
The tiles are all Ok and are secure (ceramic tiles backed on screed-ed walls and non-slip floor tiles) so I am wanting to re-grout, what do I need to do?
Thanks

 

[chappers]

rake out the old grout first then re-grout, might be hard to shift if it is two part epoxy