
gardengoth |

By RAW, no you can't - your spells known are fixed. But your GM may allow it as it's unlikely to have a big effect on balance. Remember as we'll that you can swap a spell at even levels so if you have your eye on a 4th level spell and one of your old ones is a bit dusty, that might solve your problem.
I reckon you'd be better off knowing the most higher level spells you can, and obtaining scrolls or wands (etc) to fill any gaps in your repertoire.
As an aside you can of course use your high level spell slots to *cast* lower level spells if so desired.