D-Link dir-882

i know its an old router but,

WLAN Hardware: 2x MediaTek MT7615N

how can i configure both radios to work at 5ghz

The radios are probably configured by design such that one operates at 2.4G and the other at 5G. You won't be able to change that.

What is your specific goal?

having two 5ghz radios will be able to manage channels and interference better. each radio will be using a different channel. since both radios are the same i was thinking. in any case they share the same antennas both. and the dir-882 is a 4x4 mimo device. alternatively some might want two 2.4ghz radios on the same wifi router/access point

Having two radios blasting out 2 different channels on the same band isn't really going to manage things any better. A proper site-survey + manual channel selection, followed by monitoring the performance and performing periodic scans will ensure you're well tuned. Or, use the auto option which is less predictable but typically works to select a channel that is not super crowded.

Also, use lower channel width options -- 40MHz instead of 80MHz or 160MHz will help reduce the interference/noise from neighboring APs.

the dir-882 is capable of 160mhz channels

The wider the channel width, the more likely you are to experience noise and interference from neighboring APs. Therefore, reducing the channel width is recommended.

even with today's standards dir-882 is up to the job and it's faster than the ax23

I never said that it wasn’t a good device. I’m just stating the physics and considerations about channel width and interference/noise.

i am still using it. 5ghz band has may 80mhz channels. more problematic is the match of wifi adapter to router in my experience. dir-882 still works great with many newer ax phones.

It has to do with the overlap of the channel spectrum.

If you’re happy with the performance you are getting now, no need to change.