Fill all three slots under Number 1 (where you can have the numbers 1, 2, 3, and 4 set to load functions). Now you can drag and move Number 2 left to replace Number 1, and suddenly Number 2 will have all slots accessible. Meanwhile, Number 1 doesn't lose any of the loaded functions. This makes it easier to max out individual function sets without having to level up your character.
Agency() - Complete each Agency Test
Align() - Achieve User Level 8.
Anything() - Deal at least 1024 damage in one Turn() in the Practice Test.
Bet() - Complete five encounters with one or more Limiters in use.
Bracket() - Confront Royce beyond Cloudbank.
Bye() - Complete the story.
Contest() - Clear every Test.
Dare() - Complete five encounters with five or more Limiters in use.
Drive() - Reach the Goldwalk District.
Everything() - Deal at least 2048 damage in one Turn() in the Practice Test.
Find() - Inspect 10 completed Function Files.
Focus() - Achieve User Level 16.
Function() - Unlock every Transistor Function.
Goodbye() - Recurse through the story.
Kendrell() - Confront Grant and Asher at Bracket Towers.
Limiter() - Unlock every Process Limiter.
Memory() - Unlock 32 MEM.
News() - Use 10 different OVC Terminals.
One() - Achieve User Level 24.
Performance() - Complete each Performance Test.
Planning() - Complete each Planning Test.
Process() - Inspect all completed Limiter Files.
Reisz() - Confront Sybil at the Empty Set.
Reveal() - Inspect all completed Function Files.
Risk() - Complete five encounters with all 10 Limiters in use.
Sandbox() - Clear one of each Test.
Search() - Inspect five completed Function Files.
Self() - Upgrade a Function with a copy of itself.
Speed() - Complete each Speed Test.
Spine() - Confront the Spine at the Bracket Towers facade.
Stability() - Complete each Stability Test.
Stack() - Create a Function combination requiring 12 MEM.
User() - Unlock every Upgrade Slot and Passive Slot.