how would i clear attributes?
so that when a number decreases, the old number goes away to clean up the bottom of the screen.

This is just what I do and maybe it's not the best way and/or answer. I have a few questions first though. What do you exactly mean by "clear?" I use a individual status section(A link to the status section is listed in the bottom of every section). I tie it in with my master code.
So you end up with something like this:
((Either allowing the character to skip to chapter 1 or to check current stats))

Click [[Here]](Chapter 1) to begin or [show stats].

[show stats]:
Name: {textline}

Gender: {gender}

Nanites%: {nanites}

Psionics:{psionics}

Link%: {link}

Now lets say they pick up a crystal that increases there psionics;
@inc psionics 5

Now they use kinetic push
@dec psionics 5

((This is the master section. I am working on a sci-fi at the moment))
[[]]:
@set nanites=0
@set psionics=0
@set name={textline}
@set link=0

I believe the master list will track it as a whole. Meaning you don't have to "clear" the attribute or list. I don't know if that answers your question or if it really helps in the first place......but I gave it a shot? It seemed to be the easiest way for me as the creator and for the player to track that kind of stuff. Hope it helped.