Tips on vim-surround shortcuts

A couple of tips i always forget in everyday work.

Replacement of the already surrounded block, for an instance:

text 'hello' text  
-----------------

cs'" 

will became:  
text "hello" text  

Replace tagged surrounds:
cst' tags will be replaced with '

Remove quotes:
ds'

Surround selected text:
S'

About tags:
Replacemenet/surrounding can be made by whole string, such as <code>.