You simply cannot on the TyTN II; if you want to use any version of Windows Phone from 7 and above, you need to buy different hardware.
And the same goes for an upgrade from Windows Phone 7.0, 7.5 or 7.8 to a version 8.x (and above): needs different hardware because of kernel changes.
Well, "buggy" and "obsolete" mean different things, so I'll answer them separately.
Is Windows phone buggy?
Not really, unless you opt-in to the Windows Insider programme and choose the Fast Ring, which is the first to get the latest versions and new features, but is not guaranteed to be completely stable and suited for daily usage. If you're worried ...
I wouldn't recommend starting on Windows Phone, since that's dead. Instead go for Windows 10 UWP apps. You will need Windows 10 to do this. Here are some points I'd start with.
Get a developer account
Instructions can be found here.
Get your PC ready for development
Go to Settings > Update and Security > For Developers and turn on Developer Mode.
No, Windows phone not obsolete, not buggy (comparing with Android, which I used before).
But it has only 1% of market.
And reason for this: not so much app for Windows phone comparing with Android and iPhone.
For example, we don't have Google Map, Google Hangout and even Pokemon Go.
And reason for this: developers don't want to develop app for Windows ...
The app's not working on my wife's 930, and hasn't been for some time. I think TrueCaller dropped support for Windows Mobile a little while ago.
I've told her to use the built-in Blocked Calls feature whenever she gets a call from a scammer, but TrueCaller was great for this while it was still working.
Windows Phone is not dead. It's a great operating system on great devices.
It just takes more people showing their phone and using it.
It sometimes feels like some users are afraid to tell that they have a windows phone, just because of the word Windows. Don't listen to these hipsters with iPhones saying it is something bad.
We are now busy creating new ...
Third-party apps aren't generally granted enough permissions to do a reboot, so I don't know of any Store apps with this ability, but you could do it with a sideloaded (homebrew) application.
Alternatively, there are a few operations that require the phone to reboot after doing them. For example, changing the display scaling factor (Settings -> System -> ...
The most important requirement: to develop for Windows Phone 8, you must have computer with Windows Phone 8. To use Windows Phone 8 emulator you must have Windows 8 Professional on your computer. Also you can test apps on Windows Phone device, but you should unlock device at first.
To publich apps on Windows Store you should buy an account, but it is free ...
No, you can not disable the animation effects when switching between apps - because this time is actually used to load / "unfreeze" the app and make it usable as soon as it is fully displayed.
The animation basically masks the load time - without it the system would feel even less snappy.
I wasn't able to find a source specifically for Windows Phone but ...