WtA 20th Anni. Edition, p. 244 (emphasis mine):
"With one exception, players cannot increase Background Traits with experience points. Only Storytellers can increase or decrease Backgrounds through the course of play. If the character gains a new (Storyteller character) friend through her ecological charity work, her Allies Background increases. Vice versa, if a key friend is killed by a Pentex First Team, the Allies Background might need to be decreased or removed altogether. If the player wants to actively increase a Background, you should work with them to provide opportunities in gameplay to try to do so. It can be as simple as holding a job to increase Resources, or as complex as a series of spirit quests to find new Ancestors. You don’t necessarily have to provide a checklist of tasks for players to accomplish in order to get the desired increase, however — it all depends on the Background in question and the current state of the chronicle. The Totem Background is an exception, however. Any pack member can spend experience points to strengthen their totem (and the totem spirit is likely to notice which pack members are more devout). You should still work to provide roleplaying opportunities for the players to show how they are helping to improve their pack totem, but once they have done so, each point in Totem costs two experience points."
