How to backup without encryption ?

Unfortunately you cannot transfer to a new backup unless you have the old backup password. The encrypted setting is saved on the iOS device - to remove that you must disable it via the iTunes backup setting. Any new backups from that device will also be encrypted.

If you are certain you want tot delete the old backup…

Open the iTunes preferences, select the Devices tab. Delete the old backup. This will remove it totally. I'd suggest you take a full backup of the system before doing this incase you do remember the password & need to access that encrypted backup.

I can't see anyway for you to migrate the iPhone 4s data without the original backup password - that is the point of the password - to secure a device & the copied data.

That information is no help - you need the password if you want to use the backup that you encrypted.

See what Apple say about it…

About encrypted backups in iTunes - Apple Support

What if I can’t remember the password for my encrypted backup?

You can't use an encrypted backup if you don't have the password.

When you try to use a backup, you might see a message saying "The password you entered to unlock your backup was incorrect." This message means that the iTunes encryption option was turned on in the past by:

• Yourself
• Someone who set up your device or transferred your data to a new device
• An installed profile (for business or education devices). If you're using an installed profile, contact your system administrator.

If you don't have your password:

• If someone else set up your device, check with them for the password.
• Try using an iCloud backup instead. If you don't have an iCloud backup, you can make one.
• If it's still relevant, try using an older iTunes backup

I don't know if the iCloud backup will help at all but you cannot use a backup that you do not know the password to. You cannot disable backup encryption without the password. I suspect iCloud backups may restore the backup encryption to the device but have not tested it, it seems to be your only hope.

It seems simple really, if you set a password to protect your data you can't just decide to turn that protection off without knowing the password, otherwise any thief could do the exact same thing & the security would be worthless.

Also see this for general info…

About backups in iCloud and iTunes - Apple Support