Can you change your Wi-Fi password from your iOS devices or no?

I have a iPhone and I'm wondering if I can change my Wi-Fi password from it?

No. You have to have a Physical connection to the Wi-Fi router, by Ethernet Cable, from a PC.
Most routers will not let you change settings over the Wi-Fi link by default.
but once you in the Settings you can allow connections over the Wi-Fi link.

It depends on the router, but for best results, it's always best to use a direct, physical connection to your router.

My Belkin F9k1109 router let's me perform all changes both through Ethernet and through Wi-Fi.

Now, as you should know, once you hit "apply", "Save Settings", your iPhone will no longer connect to your Wireless network. It may ask you to type in the password, or you may need to "forget" the network and join it again with the new password.