Q: iPhone 6

What kind of passcode? is it the restrictions passcode, or did you forget your passcode?

To remove a restrictions passcode,

• either restore the iPhone up as a new device, see: How to erase your iOS device and then set it up as a new device or restore it from backups - Apple Support   https://support.apple.com/en-us/HT204686
• or restore it from a backup you made before the restrictions have been enabled, see: How to back up your devices using iCloud or iTunes - Apple Support

Restore the iPhone as a new device. Then you can set up the passcode in the settings to the same code as your old iPhone. After that restore again from the iPhone 5s backups.

if you do not know the correct passcode you can only restore to factory settings using iTunes on the computer you synced the iPhone with:

https://support.apple.com/en-us/HT201252

https://support.apple.com/en-us/ht204306