It is hard to upgrade it. you have two ways if you have enough money and some luck
1- try your luck at Artisan wind in Twin city (422,355) and put meteors but it will cost you lot as the wrong upgrading reduces durability.
2- at weapon master(180,192) at market you can give him Db to upgrade it fast.
if you have not db and have bad luck Like me
try to exchange it in market but hint it must non free (bound) item
first if you need luck you should have many luckytime 10 or more
2-Buy 2 mets scroll and go to twin city and try upgrade them if not repair them and try again good luck
3-if you have dbs you can go market to weapon master and he will help you