Your text file may contain HTML or XML like this.
Then, you want to delete or change text inside tag which is p tag for this example.
To delete text inside tag, in Vim normal mode, move a cursor to be inside tag and type this command.
This command refers to "delete inside tag".
To change the text, just change "d" to "c".
"change inside tag"
You can apply this to any command just relace d. For example