Buy Grand Fantasia Online Gold to upgrade, which is not enough. You should have a guide to tell you some tips during upgrade. I share my experience of leveling 20 to 40.
There is really no easy way to go about this, but I can give you some suggestions to make this whole process quicker. First off in adventure plane the fisherman M gives you a quest about mushrooms or something this is the Luna quest do this quest as much as possible as you go through the game, it will give you loads of experience, gold, and items.
Now that you are at level 20 you are going to want to train just outside of Zandt. Kill Woody until they are not longer yellow. At this point you want to move onto Hill of Wind here you want to kill either beetle bugs or red formic. You do not waste your time on the guards they always take a bit longer to kill and give almost no experience compared to the attack monsters.
Once these become somewhat easy for you, you can move onto Levis start of with the regular ones until they are no longer a challenge.
Next you move onto Elverson. If you decide to train here kill turtles like crazy, it should be very easy for the hawker class because the attack of turtle is very slow. Once turtles become somewhat easier you can move onto aqua.
If you decide to move onto aqua do not waste your time in Elverson the aqua spawn is way too crowded and you are kill stolen constantly. Move onto anima, the aqua are located by the northeast spawn point and you have a chance to attack the aqua king.
When you reach level 30, you are sure to go to Junco and join a union. Whatever union you join you are going to want to do all the quests that are easy for you from them, you want as many union points as possible.
Continue on aqua until you are close to level 40 even though they become very easy you can kill them very quick and the aqua king still gives decent experience.