best way to inform the user about newly released application.?

Question

hi...
i have released one application..

now i have to maintain the document for the released application..

which is the best method to write the information
such as in word,or pdf or excel or
is there any way to keep the document..?

so that every one should know that the new release
application is released .. and they should be updated

i've hosted the previous application and now i have
release the modules in that application ..

now i have inform all the user that we have
released new modules with etc etc features ..

which is the best way to inform the user about newly released application..?