After logging into your account, select Finance from the left panel on Yahoo's Home Page. This will take you to Yahoo Finance home page (http://finance.yahoo.com).
Click on "My Portfolio" in the Menu Bar and then Create Portfolio.
Look for "Import". Click on "Import".
In the Import window click on "Choose File". Find the file, then double-click on it to select it for import to Yahoo!, and Submit button. After the page refreshes, you will have uploaded your portfolio to Yahoo!
The final step is to rename your portfolio on Yahoo!'s website: Click on "Settings" then Rename.
That's it... you now can monitor your portfolio from anywhere in the world!