This will remove the users tag and everything in between the users tag:
```bash
sed -i .bak '//,/<\/users>/d' users.xml
```
A backup will be created named users.xml.bak.
If you want to select only specific tags use this:
```bash
sed -n -e '//,/<\/private-parts>/p' e users.xml
```
For more advanced XML processing use:
\* [XMLStarlet](http://www.ibm.com/developerworks/library/x-starlet/index.html)
\* [xml-coreutiles](https://github.com/rudimeier/xml-coreutils)
\* [xml2/2xml](http://www.ofb.net/~egnor/xml2/examples)
\* Your imagination.