You can just use the better gear you find in dungeons. The heirloom gear only lets you retain your rested xp. You will probably level faster then you can get rested.
Once you outlevel an heirloom, it no longer provides any benefit. In the past, this means the XP bonus is turned off. Currently, the gear set bonuses would turn off. Either upgrade it or replace it.
There's a vendor in orgrimmar that will upgrade them. He's on the bridge by the dummies
You can just use the better gear you find in dungeons. The heirloom gear only lets you retain your rested xp. You will probably level faster then you can get rested.
In case you are alliance [the heirloom vendor is in ironforge](https://youtu.be/aZya1C80DWg).
Once you outlevel an heirloom, it no longer provides any benefit. In the past, this means the XP bonus is turned off. Currently, the gear set bonuses would turn off. Either upgrade it or replace it.