When redesigning an existing concept, all the steps of concept design really become clear. Let's take this Vision as an example.
First you need to get informed about the character. Vision's background tells us he was created by Ultron as a weapon against the Avengers, constructed from a recycled human torch body (a synthezoid) into the android we know now. And here are his different incarnations through time:
Then, by comparing looks you can notice the patterns, the repeating icons and colors, you can pick the elements that truly speak of the character.Here are the visuals i choose to keep:
-Dark face
-Head gem
-Head gem
-Diamond icon
-Collared cape
-Green-red-yellow colors
Last but not least, you can identify the characters skills and capabilities, in case of superheroes, his powers. The vision can alter his body mass and density from weightless and incorporeal to megaton heavy and hard as diamond.
Now we're set for adding some personal ideas and changes that will make the character look somewhat different yet remain easily identifiable.