How to upgrade from Ubuntu 14.04 (32-bit) to latest Ubuntu Budgie (64-bit)?

Ubuntu 14.04 (32-bit) is installed on my laptop along with Windows 7. I have barely used Ubuntu, but I’m on it now since Windows is troubling me.

I was looking for a Ubuntu flavour that is light-weight, and I found Ubuntu Budgie, which is also pretty sweet looking, hence I opted it.

I’d be highly grateful to you, shall you could give me exact steps on how I can update to the latest version of Ubuntu Budgie (64-bit version.)

Please let me know if I need to update Ubuntu 14.04 as well.

Note:

-When I was trying to update the OS using Software Updater, I would get the error, “Requires installing from untrusted sources.” And I’d have two options, “Settings…” (which leads to the Software Updater) and “Close”.

Related Queries:

-Does all the flavours of Ubuntu require the ‘original’ Ubuntu to be installed, or they are stand-alone operating systems?

-I need an operating system which is ligh-weight and can run most Windows softwares. Is Ubuntu Budgie a good pick or should I go for something else?

Memory: 3.9 GiB

Processor: Intel Core i3-2350M @ 2.30GHz x 4

Graphics: Gallium 0.4 on NVD9

OS type: 32 bit

Disk: 47.3 GB