To cast one of these spells, you must expend a slot of the spell’s level or higher.
(Chapter 3: Classes, paragraph Preparing and Casting Spells, in the Class descriptions for both Cleric & Wizard.)
This is expanded upon in Chapter 10: Spellcasting, under Spell Slots, p78
When a character casts a spell, he or she expends
a slot of that spell’s level or higher, effectively “filling”
a slot with the spell. You can think of a spell slot as a
groove of a certain size—small for a 1st-level slot, larger
for a spell of higher level. A 1st-level spell fits into a slot
of any size, but a 9th-level spell fits only in a 9th-level
Only some spells specify an increased effect from using a higher slot. All others have the same effect regardless of which level slot they are cast in.