So it means i must use the weapon till 255 times ?
and if it fail upgrade weapon level are the weapon gonna break / gone ?
and are the material is hard to find ?
Yes, it requires you use the weapon no less than 255 times.
If you fail to upgrade the weapon, the only thing you lose is the ore you tried to upgrade it with.
Ore is pretty difficult to find, but it's not impossible. If you can't find any, you could just buy some from the Antique Dealer (this requires real money. However, you should get 10 ore for completing a quest if you talk to the guy near the community forge, loom, and pot in the market. Make sure you talk to him if you haven't already.).