The mk6 GTI has a timing chain, not a belt, so shouldn't need changing - in theory, the chain is a non-serviceable item.
Although the chain shouldn't need changing, VW made a number of revisions to the timing chain tensioner over the life of the mk6 GTI as there have been a number of tensioner failures. So, if your car still has the original tensioner it might be worth considering changing it to the latest version. Have a look at the 'Timing Chain Tensioner Failure list' sticky at the top of this (the mk6) section of the forum.