Help formatting and updating a Blade C2

[Viper8797]

Hello!

So, i have a ZTE Blade C2, sold in my country (portugal) as a MEO SMART A12. The phone's version is android 4.2.2. It is rooted (I have no idea how I did it, or how it actually even worked, involved using some Chinese app)
I am not very good with phones, mostly a pc dude, so I am largely ignorant about everything

So, I now wish to format the phone and update it to the latest version of Android, which I think is 4.4(?) Right now, if I try to use the "Search for Updates" on the phone, it reboots the phone and I get a error notification, which I assume is due to the rooting.

So, I come to thee, to help me on my quest. Here are my main questions:

• How can I format my phone and update it to the latest android version? Are there any problems with it? Device slow-downs, anything?
• What's the best way to root your phone after said update?
• What must have apps, launchers, ROM thingies (not even sure what a ROM is just heard about it (and everywhere in the world smart smartphone people cringed hard))
• Can I get my SD card to store apps etc? Right now it cant, the phone's memory is divided into Internal and phone memory. odd

Thank you and sorry again for being such a noob. If this is not in compliance with some rule please let me know, I don't really want to write this all again.