/usr/share/dict/web2 question

Hello,
I'm very new to this, and I'm hoping that this is in the right forum.
How can I add extra words to either of my /usr/share/dict/web2 or web2a files?
I am using software that accesses these two files and would like to expand them.
I thought that I could simply change permissions to "Read & Write" and add words,
but I am still not allowed to save the file: "you do not have appropriate access privileges."
I guess that it's a safety measure?

Thanks if you're able to offer some help.

Rod