Change the size of width in yas-describle-table

Question

Upon checking yas-describe-table, I find

state name                               key 
#+ATTR_HTML: :width ..                   width

Click into it

# -*- mode: snippet -*-
# name: #+ATTR_HTML: :width ...
# --
#+ATTR_HTML: :width ${1:500px}

I plan to change the size of width from 500px to 700 px, but it prompts that

cond: Buffer is read-only: #<buffer width>

How could change the size of width?