[prashantj21]

I have NL520 with a Microsoft account. I need to change it with different live mail.
If I go to Settings > about > Reset my phone, will I be able to do that?
Important thing is I installed the updates (8.1 and Cyan) yesterday. I don't want to lose those updates; otherwise I'll have to download those updates again. So is it possible to change the default account without losing updates?

[Maaz Mansori]

Yes, resetting your phone is really the only way to change your Microsoft account and you will not lose any updates such as 8.1 and Cyan you have installed. You will, however, need to change your settings manually and download all your apps again and if you paid for any, you will need to pay for them again because you are using a different Microsoft account.