Both Could and Might express a possible outcome.
she could change her mind.
she might change her mind.
Both could and might are interchangeable most of the time, but
Might is generally used with negatives..
She might not come today...YES
compare...she could not come today..NO
""could"" is proper when the sense of the sentence requires it to mean
"able to"
he got the degree so that he could find a better job
John anulled the marraige with Lisa so that he
could marry Rachel
Would
You use
would to express willingness or promise.
Compare with the first two sentences
She
would change her mind....Poor..
John agreed that he would do it...Good
Lisa promised that she would return before dark.
I would be interested in your offer.
And to express habitual action in the past
We would walk along the canal at night.
We would fight a lot when we were children.
good enough?