Avoid Visio at all costs.
If you have a computer with Visio installed on it, pull the plug and run as fast as possible to the nearest fallout shelter.
There are many, many, MANY open source UML projects that are available free of charge that work much better than Visio.
Do a Google search for "UML Tools" and you'll see. Download a couple of them, see which one you like best and use it.