Casting a Spell at a Higher Level

When a spellcaster casts a spell using a slot that is of a higher level than the spell, the spell takes on the higher level for that casting. For instance, if a Wizard casts Magic Missile using a level 2 slot, that Magic Missile is level 2. Effectively, the spell expands to fill the slot it is put into.
Some spells, such as Magic Missile and Cure Wounds, have more powerful effects when cast at a higher level, as detailed in a spell's description.