Guide upgrading to gdr3 ?

[Ariel Aouizerate]

Can someone give me a guide to that ?
By the way is it erasing everything ?

 

[Nokia Boy]

i think it's not officialy released for lumia 520 yet but you can try the GDR3 Developer OS Preview
A few notes first:
There are a few key items that you must understand before you update your phone:

After you install a preview update, you may void any warranty from your mobile operator and OEM.
A preview update only includes the Microsoft portion of the update; mobile operator and OEM driver updates will be available when the official update for your phone is available.
You cannot revert or return to a prior operating system release version after you have updated your phone to a preview update. We will move you forward to a "released state," but we cannot take you back to a prior "released state."
Step 1.Get an app studio account: Windows Phone App Studio | Microsoft use the same email as you used for your phone....
Step 2:after you make an app studio account, access that link from your phone and download the app: Preview for Developers | Windows Phone Apps+Games Store (United States)
Step 3 After it get installed,open it and login with your account and enable Developer preview updates
Step 4 Go to options and check for update,voila...now you can download and install GDR3 update preview