From the CiviCRM home page, click the CiviPledge Link
If it was a recent pledge, look below and find the pledge. For example: go to Peter Jones, then go all the way to the right and click the cancel link.
If it was not a recent pledge, click the Find Pledges Link, enter the pledgers name or email and then click the search button.
As indicated by the orange triangles, there are many other ways to find a pledge. After entering known information, click the search button.
For example: enter Zoe Zanzela for pledger name and then click the search button. (view below image)