Characters wishing to level up as a new class are limited to classes within their own stock. If you’re using the basic rules, this means the option to switch classes is only available to human characters.
To do this, you must first learn all the skills belonging to that class. The rating doesn’t matter, knowledge of the skill is enough. You must also follow any special rules belonging to that class, such as alignment restrictions and limits on ability ratings.
Example: a 3rd level cleric who wishes to become a paladin at 4th level must first learn Orator and Rider (as clerics already have know the Fighter, Theologian and Ritualist skills). The actual ratings for abilities and skills doesn’t matter as long as the special paladin rule is followed. As a paladin, the character must be Lawful and cannot have a Health rating higher than their Will.
The character remains at the new level but only gains the earliest level benefit for the new class. In the above example, the cleric-turned-paladin is now level 4 but gains the level 1 paladin level benefit (in this case, access to a greater variety of weapons). You do not gain the trait of the new class, though it may be earned during Winter phase when traits are gained and lost.
Level requirements are per the character’s total level.
Example: A 3rd level cleric becomes a paladin. They’re now a 4th level character (cleric 3/paladin 1) To reach level 5, the character must spend 22 fate and 12 persona. At that point the character will be cleric 3/paladin 2.
Characters may switch to other classes or back to their original class. When gaining benefits, you’re limited to the lowest set of benefits you haven’t yet chosen.
Example: If the cleric 3/paladin 2 wants to continue as a cleric at level 6, they gain the benefits for a cleric 4.
A character’s total levels cannot exceed 10. Characters may not dedicate themselves to more than two classes.
Example: The cleric-turned-paladin continues to train as a paladin until level 10. When this is reached, they cannot continue to advance their level. They will eventually retire as a cleric 3/paladin 7.
Characters who switch to a magic-using class (ie: magician or cleric) will learn to cast spells or invoke prayers as per the new class’ level 1 benefit. Characters who switch out of a magic-using class retain their magical abilities. Thus it’s possible for a level 1 magician to be able to use any weapon or armor if they switch to the warrior class.
Note: A character forced to leave their class (ie: a paladin whose alignment changes) loses their level benefits and becomes a new class of the same level (choosing appropriate level benefits for that class). These characters are not considered to be dual-classed.