My first advice is: go to a luthier.
If you want to go for it yourself:
First try to turn up the bridge saddle. Note that thicker strings need more height. If the buzz continues, lower it back to the original position. If the neck is overstretched, there may be fret buzz caused by the lower frets and that won't go away by heightening the bridge.
A neck may be adjusted to a sniff hollow. If you press the string on both ends behind a fret, very little room between the string and fret 8-10 is not bad.
Wrenches can be bought in any hardware shop.