Freeze him when he opens his mouth, watch out for fireballs.
He will shoot an arm at you, freeze it then attack it with your attack spell.
Repeat process

Hi
The answere to your question is
1. Run around in circles and keep out of its way
2. When it has its back to you try to freeze it with the Glacius spell
3. It should turn around and face you
4. Then it should open its mouth and shoot fireballs at you
5. After it stops shooting at you, it will keep its mouth open for a few seconds
6. While its mouth is open, try to freeze its mouth
7. If you succede, its arm will come off and come flying towards you
8. Run to your right to dodge it, but be careful, it follows you
9. When its arm is on the ground, turn to face it and freeze it
10. Repeat from one to nine
11. Now it should only have its legs left ( if not you've done something wrong )
12. When it walks around you will see pink circles on the floor around his feet, stay away from them
13.Now when it shoot, it will only shoot one at a time
14. Keep freezing its back and eventualy it waill fire five times
15. Repeat number six
Now you should have killed him
P.S. Make shure you're Hermione befor you thry to kill him
Good luck and a good question