Talk to the Skill Master at Gretycos Castle (Rogwel) or Cerity Praha Castle (Elerd) to reset your skills.
From level 1 to 30 you can reset all your skills a total of 10 times.
When you reach level 31, you lose any remaining skill resets and can reset all your skills one time.
There are skill reset scrolls that dropped from a prior event that allows you to reset one skill one time.
Elerd Skill Master
The Elerd Skill Master Erkerano can be found next to the Warehouse Keeper in the Merchant Road area.
Rogwel Skill Master
Skill Master Berit of Rogwel is found near the Warehouse Manager at the Gold Road at Gretycos.