You might take a look at the manual.
https://www.tp-link.com/de/support/download/tl-wr902ac/
Choose hardware and software version corresponding to your device. Update software version off possible.
When you access the wr902ac you get an option for quick setup. That might work regardless of the switch-position.
That’s the easiest way.
On some older versions 5GHz for client mode wasn’t available. Should work for HW v4, software v4.
As Eric wrote improvements in sound quality can be expected. but depends on „upgrade-level“ and of course your current situation/set up.