There are two ways to delete tickers from portfolios.

One way is to go to "My Portfolios"
Click on the name of the portfolio that you want to delete a ticker from.
That will take you to the "Summary" of that portfolio where you will put a checkmark in the box to the left of each ticker you want to delete. That will bring up a "Delete Tickers" button in the upper right, click "Delete Tickers"
You will be asked to "Confirm Delete"

The second way to delete a ticker from a portfolio is, when viewing a graph on a company, go to the "Add to Portfolio" button in the upper right corner, click, that will produce a pop-up letting you know what portfolios, if any, you have the ticker in, OR if you want to add it to any of your portfolios. Complete by clicking "Save changes"