Odin the the program that transfers the new firmware to your phone.
The most important thing to do in Odin, is ensure you check the relevant boxes before upgrading
Within Odin Left hand side window
[x] One Package
[x] Reboot (ticked)
[x] Protect OPS (ticked)
[x] Reset Time (ticked) 300
[ ] Debug (not ticked)
Refer to both the video and the guide instrutions and you should have po problem.
Phone: Galaxy i9100 SII: Now using Galaxy TAB7.7. Sowheat!!