I... am not sure what you're asking. You don't memorise spells of a particular level, you have a set number of spells that you can prepare. The up-leveled ones are the hotkeys to cast the spells at a higher level, but you always can only prepare your level plus your casting mod spells (so at level 1 you have 4 spells prepared with 16 in your casting mod, 5 at level 2, etc) and upcasting doesn't require a separate preparation, it just casts the same spell with a higher slot