How do I properly alter this quote?

You're quoting a fragment which is probably part of a complete sentence. I'm guessing that you want to incorporate the fragment in your own sentence, that you need to change (at least) the one word to match the grammar of your framing sentence, and that you wish to quote the fragment so that the original author can be credited for his exact phrasing.

If the original looks something like this:

- It was a long night. We were trapped, exhausted, and half-blind with fear. It wasn't until dawn that we staggered up from the filth of our wallowing.

then your quote might look something like this:

- These characters find themselves unable to "[stagger] up from the filth of [their] wallowing" in the darkness of the night. (Johnson, p. 56)

Any alteration you make to the original text should be marked with brackets. Additionally, any change you do make must avoid changing the original author's intent and meaning. Finally, the original author must be credited in some fashion.

I think that sounds right. The stagger part.

You altered it right.

You can't alter it. If it's a quote, it must be exactly as the original. You may paraphrase it.

"Staggering" is a struggling step. "Wallowing" is lying in mud or dust.

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