d6300 modem router connecting to orbi

There is a simple switch on the side to turn off the wifi. But you do not need to disable the wifi on the D6300. (With a different SSID, your wifi clients can use the Orbi.)

You might though find it useful to disable the router bit of the  D6300 ( and put it into "bridge" mode) or the Orbi. Two routers on one network can cause headaches.

When to put modem into bridge mode | Answer | NETGEAR Support

There is a manual for the D6300 somewhere at the end of this link:

>>> D6300 | Product | Support | NETGEAR <<<

Unfortunately, unlike some modem routers, the D6300 doesn't have a simple "software switch" to disable the router bit.

How to configure two NAT capable devices | Answer | NETGEAR Support

It is easier to put the Orbi into AP mode. (Check the manual.) It may also be preferable, depending on how you now use the modem/router, the number of wired LAN connections for example. But the D6300 does have a problem on that front. According to Netgear's manual for this device the LAN and WAN support only 10BASE-T or 100BASE-TX. That makes it slower than many newer internet services and most modern network hardware.

I'd be tempted to invest in a new modem. I did that to pension off my D6400, a more capable box than the D6300. The DM200 is dead cheap.