If you don't want to buy a new smartphone, your best solution is to install an unofficial Android firmware on it.
Android is open-source, so it’s possible for Android users to take its source code and roll their own operating systems – known as a custom ROM – for their smartphones. CyanogenMod is the most popular community-developed ROM for Android. Don’t worry you can choose any other update as long as you are ensuring that the system is stable and without bugs or things that aren’t working properly.
To upgrade, users usually have to back up the original operating system and then "root" the phone, or disable the security settings that protect its OS from being modified. Keep in mind that installing the system incorrectly could render the phone inoperable, and that running an unofficially supported OS could void the phone manufacturer's warranty.
1. Install at your own risk
2. Choose your custom ROM
3. Root your phone
4. Back up your current firmware and phone
5. Prepare Google’s default android apps for installation
6. Install the custom android firmware
7. Enjoy your new android phone!
Each phone can have its own unique steps for doing this, so you should follow instructions for your specific model. You'll find them on the Custom ROM webpage or some Android forum.