If you have Vim surround with plugin installed, you can use a powerful command of surround with to add or remove character around a word.
For ys, you can remember as "you surround".
Surround the word hello with double quote
yse" or ysaw" or ysw"
For cs, you can remember as "change surround.
Change surround character from " to '.
<visual mode selection>S<character>
Select world hello with visual mode and then surround with character ".
Select to the end of word, then surround with '.
Delete a surround character ".