The Drow High Magic racial feat (XGtE, p. 74) states:
You learn more of the magic typical of dark elves. You learn the detect magic spell and can cast it at will, without expending a spell slot. You also learn levitate and dispel magic, each of which you can cast once without expending a spell slot. You regain the ability to cast those two spells in this way when you finish a long rest. Charisma is your spellcasting ability for all three spells.
Note the almost identical wording in the Magic Initiate feat (PHB, p. 168):
[...] In addition, choose one 1st-level spell from that same list. You learn that spell and, using this feat, can cast it at its lowest level. Once you cast it in this way, you must finish a long rest before you can cast it in this way again.
And then read the Sage Advice ruling on casting these kinds of spells using spell slots:
If you have spell slots, can you use them to cast the 1st-level spell you learn with the Magic Initiate feat?
Yes, but only if the class you pick for the feat is one of your classes. For example, if you pick sorcerer and you are a sorcerer, the Spellcasting feature for that class tells you that you can use your spell slots to cast the sorcerer spells you know, so you can use your spell slots to cast the 1st-level sorcerer spell you learn from Magic Initiate. Similarly, if you are a wizard and pick that class for the feat, you learn a 1st-level wizard spell, which you could add to your spellbook and subsequently prepare.
In short, you must follow your character’s normal spellcasting rules, which determine whether you can expend spell slots on the 1st-level spell you learn from Magic Initiate.
In other words, to cast these spells using a slot, you must follow Sorc's spellcasting rules:
- You know the spell (again, Drow High Magic says "you learn" these spells, same as Magic Initiate, but different from the Drow Magic racial ability, which says "you can cast...")
- It is a sorcerer spell.
- You have the slots available.
Similarly, the rules for replacing Sorcerer spells state:
Additionally, when you gain a level in this class, you can choose one of the sorcerer spells you know and replace it with another spell from the sorcerer spell list, which also must be of a level for which you have spell slots.
So, the three requirements here are that:
- You know the spell.
- It is a sorcerer spell.
- You replace it with another sorcerer spell.
Therefore, RAW, it seems possible to replace them. Am I missing something that would point to the opposite conclusion (or that explains the down votes)?