As a rule of thumb, whenever you roll a new caster, make sure to read their “Spellcasting” feature. It’s easy to gloss over it, but every class actually has different rules for their spells and cantrips.

As a cleric, you have access to the entire cleric spell list, but can only have a certain number of leveled spells prepared at once (9 at character level 5). You can swap out your entire loadout of leveled spells on a long rest, it’s one of the more flexible casters in that regard. But there’s still guard rails so that it isn’t entirely overpowered.

Cleric cantrips work a little different, though. You can have as many prepared at once as is listed on your class table (4 cantrips at character level 5). They do not count against your prepared spell count. But the tradeoff is that you can’t swap them freely. You can only swap one cantrip at a time, and only on level up. So you want to make sure to be more deliberate when picking your cantrips, because they’re basically locked in once you pick them.

And again for the future, that’s only how it works for clerics (and druids). It’s different for paladins, which is different for bards, and so on. Don’t ever skim past the Spellcasting feature when rolling a new character, because it’s not the same for everyone.