First you have make sure you are logged in. When logged in, your name is shown in the upper right corner.
Click "My Fundraisers" in the right corner below your name. You click on your fundraiser, and you should see a blue box in the upper left corner that says "Edit Fundraiser" (see attached screenshot).
Click on "Edit Fundraiser" and you can edit every element of you fundraiser.
Remember to scroll down and click "Save Changes" (see attached screenshot) in the bottom of your fundraiser page before you leave the page.