I assume you mean drive chain...the XX uses a 520 chain at 80 links, and changing it is easy..just loosen the chain and break the chain at the master link, remove old and install new chain reconnect with new master link, which should come with a new chain....if not make sure you order the right size master link. To make it easier you can connect the new chain to the old with the master link and as you pull out the old chain it will feed the new chain for you, as long as you are in neutral.
The ERT2 chain is good, that is what I use and has lasted 2 seasons, yes it is recommended that you replace sprokets with chain, but I have just replaced the chain before if the sprokets look good. If I was running a 13 and had the possibility of one day going to a 15, I would cut the chain if needed, but I would do it near the end of adjustment on the tight side so you have ample room to loosen to go back to a 15. the only problem you may run into is when the chain streches, as it will the first couple rides, if you reach the end of adjustment and the chain is still too loose, you may need to take another link off.
Another thought, if you still have the 14T, put the 14 on and cut the chain so you are at middle travel in adjustment, you should have enough adjustment to go up or down one tooth.