Remove date and author from portfolio posts

To simply have the output HTML not display in the browser, these elements can be hidden in CSS with:

#content .portfolio .entry-meta {display:none;}

If you want the elements to not be output in HTML, you will need to customize the portfolio page template. IF that is what you want to do, use Pastebin to share the full code of the portfolio page template and we can take a peek.

To discover what CSS is output by your theme, use a web inspection tool such as Firebug: http://getfirebug.com/ , Chrome Inspect Element: https://developers.google.com/chrome-developer-tools/ or Internet Explorer 9+ F12 Dev. Tools: http://msdn.microsoft.com/en-us/library/dd565627(v=vs.85).aspx#csstool

There are others.

When editing CSS, use a Child Theme
http://codex.wordpress.org/Child_Themes
Custom CSS Plugin, or Theme provided custom CSS option.
Edits to parent themes are lost on theme update.

Learn CSS: http://www.w3schools.com/css/