Finally I bought my first lumia, although I already had an android device. At first I wanted to buy lumia 520, since it was cheap. After browsing more and more, then I decided to buy lumia 620 which was also cheap enough, but a little bit more expensive than 520. Because it had a better camera. Lumia 625 also had front camera (for selfie :p) and flash light at the back camera, but the 520 didn't. And the screen was 4,3 inches, much bigger than 520.
Then checking the software and operating system, it was windows amber. Fortunately it supported the latest windows os, which was cyan (8.1). I turned on wifi thetering in my android device. At the setting of lumia 620, I found "phone update" and the download began. After completing the download, I installed it and restarted my lumia 625. But then I checked, it was still windows amber. Any thing wrong? I might did a mistake, I thought. I downloaded and installed again, then restarted my phone. At the setting, I found that my lumia 625 succesfully had windows black os, but not yet cyan.
To make it become cyan, i did two steps as amber to black. Twice download, twice installation, twice reboot and my phone had windows cyan (8.1). Hoooorrreeyyyy!!!!