The form used to display articles is specified by the <txp:article /> tag in your page template. In the default template it looks similar to this:

<!-- center -->
<div id="content">
<txp:article />
</div>

To display articles using a different form, change the <txp:article /> tag to specify the form name like this:

<txp:article form="myform" />

If no form="..." attribute is specified, <txp:article /> will look for an article from named “default”.

You can specify separate forms for list pages and individual article pages like this:

<txp:article listform="short" form="long" />

It’s also possible to use a different form for a single article, using the Override form selection under Advanced Options on the content > write page.