Thanks everyone. Yes, indeed it seems to stuck at 0% but internally it continues downloading, and then jumps to 40%. The thing is I've left it downloading, went to sleep, and then it alerted with a sound that I had to restart. As I had to wake up early this morning and I needed the alarm function, I was afraided of the upgrade to fail and I didn't restart it, I thought "I'll install it tomorrow after awakening". Well, when I tried to install it, it's given me an error, an error that I read over here, 0x80000c05 or something finished with 5, I don't remember.
I turned the phone off and retried, and... IT STARTED DOWNLOADING AGAIN! Oh my ******* god. Anyway... Solutions to that error? Soft reset with Volume Down + Lock key, maybe?