When you are level 20, talk to Grand Master Ramos (Gludin) to become a Warrior. By l2hub
Steps from the game client
Onward Toward Your Trial
Quest that must be fulfilled in order to change occupations to a Warrior. Tell Master Aymus that you wish to become a Warrior, and he will tell you to first visit Trader Simplon in the Town of Gludio and find the 'Sword of Trial.'
Test of Spirit
To obtain the Sword of Trial, you must carry out a task for Trader Simplon. Fight the tracker skeletons in the Ruins of Agony and return with 10 of their rusted swords.
What a surprise! The rusted sword and the sword of trial are the same! Well, since you have them, take them to Master Auron in Gludin Village.
Trial of a Warrior
Using the sword of trial you received from Trader Simplon, you must defeat the Venomous Spiders, then collect and bring back 20 of their legs! They can be found on Windmill Hill in the southern plains of the village. Kill Venomous Spiders and Arachnid Trackers!