When you install the software, you specify the Standard you want to use.
This is done in a dialog that is presented during installation.
The default standard is ISO, which is a metric standard.
To set everything up for English, inch, select ANSI in this standard.
After installation, there is no single place to go to change the standard.
It all depends on you always using one standdard over another.
If you mix files, sometimes inch and sometimes metric, leave it the way it
If you need to always create the other type, the easiest way is to
Then install again specifying the other standard.
You can also simply use File-New. Click on the More tab.
Select the template that matches the standard needed to create the new file.