Help please I'm a lancer and want to be a archer too

[Nutz]

You can switch as long as you're not in a dungeon or in battle (or I suppose in a cutscene or menu as well). It's very quick. After your level 10 class quest you get the ability to join other guilds. All you have to do is walk over and talk to the guild receptionist at whatever guild you want to join (Archer's in this case). You get a quest that pretty much involves you clicking yes when asked if you want to join and then talking to the guild master. After that the class is unlocked, you get the starter weapon and you get access to another gearset.

[Sagittarian]

After your level 10 class quest you get the ability to join other guilds.

^^ Important point.