SPELLS AND LEVELS

When you start a new level, look at how many spells of each level you are able to cast. For simplicity's sake, you *can* ignore the spells you were casting earlier (because you can do that after every full heal-up, if you like). The important thing is that if your level tells you that you know 2 3rd level spells and 4 5th level spells, choose spells that match those levels.

The highest level spells you know can either be spells that have just become available to you or spells listed as lower level spells but that you are choosing to use as a higher level spell.
Let's use the 2 x 3rd level and 4 x 5th level example, from a 5th level cleric. If I decide I want to cast Cause Fear, I have to choose whether I want it to one of my 2 2nd level spells or one of my 4 4th level spells.
 
Given that the 5th level cleric only has six spells, total, I *could* make all of them upgraded versions of spells that appeared on the cleric list at 1st level. It could look like this....

Bless (3rd level)

Cure Wounds (5th level)

Hammer of Faith (3rd level)

Javelin of Faith (5th level)

Shield of Faith (5th level)

Turn Undead (5th level)

Most people don't do that, they want to access the new hotness that enters the game at higher levels. But if you're paying careful attention to the spells, there are certainly cases in which old standbys that had 1st level versions are still wonderful to cast as 7th and 9th level versions. Because we went to some effort to make it so: higher level characters get a very wide range of thoroughly useful spells to choose from.

INCREMENTAL ADVANCES

When the 5th level cleric we're talking about gains an incremental advance, he gets to cast a spell he will have access to at 6th level that he doesn't normally have at 5th level. The 6th level cleric only gets one 3rd level spell and six 5th level spells, which is now a total of 7 spells instead of the 6 spells the 5th level cleric gets.

So what I want to have happen is that the 5th level cleric taking an incremental advance can *add* a 5th level spell, so that after the first incremental advance the cleric has 2 3rd level spells and 5 5th level spells, a total of 7, the same as they'll have at 6th level, but not quite as good after the first incremental advance. Another incremental advance would be possible, I think, since the cleric gets two higher level spells by advancing from 5th to 6th. But the second incremental advance needs to remove a 3rd level spell and add a 5th level spell so that the total number of spells the cleric is casting isn't better than what they get at 6th level.