Respec is a term used to describe the Skill Reset option. Every character gets the option to reset all their skills and get their money (Archlord gold) back from the trainer but it may only be done once, so use it wisely. When using your reset, simply go up to your class trainer and select the Reset option at the bottom of the window.
Once used your character (Archlord online gold) will receive all the skill points you have used thus far along with all the money you have spent on the skills. You are now free to reselect and relevel your skills. Caution: Once this is done it can not be undone and you will no longer have the reset option.
If you have used your Skill Reset from the trainer, you can buy Return Orbs from the Chantra Shop, pressing your T key will open the shop, to reset one skill at a time. Once these are bought simply open your Skills Menu, your K key, select the skill and click the "Reset Selected" button. This can be done once for every orb you buy in Archlord.