Open Dev-C++
In the menu select "Tools" ---> "Check For Updates/Packages..."
In the window that appears in the drop down list saying "Select devpak server:" choose "devpaks.org Community Devpaks"
At the bottom left of the window click on the button "Check for updates"
A list of devpaks should then appear in the "Available updates list:"
Click where it says "Update" to order the updates by their name
When I did this I saw two options for "Expat"
Select this & click on download selected
Then just follow the instructions to install it.