On the Homepage, expand the "Leads and Opportunities" tab.
And click "Lead Management".
On that page, you will the list of Leads and Call logs, you can search for a particular leads via search bar at the upper right corner of the page or use customise filter to narrow down search.
Once you found the lead you wanted to edit just click "Quick Log" button at the end of each row.
In that page, you can edit Quick Call and put in your desired data.
You can either delete the log or edit in there. If you need to edit just press "Update" blue button and if you need to delete just press "Delete" red button.
If you need to Add a new Quick Log instead, just click the radio button saying "Quick Logs"
With Quick Logs you have the option of prompting for a follow-up activity, to do so select "Yes" is Follow On. Once done select if you want to record just the Date or the Date and Time in the Include drop-down.
Anything you enter in the Text box is what will be included on the Lead as it's activity (For example "Called no answer").