how to edit an inbox message in comcast webmail

I need to change the content of an email that is in my inbox . This should be simple but when I look it up it says what I have pasted below and when I try to follow those instructions I get a new email window and thats not what I want. I just want to change something that is already in the email and save it still keeping it n the inbox.

This window is used when creating or editing an email.

In order to open the window, do one of the following:

• Click on Compose in the toolbar.

• Select an email. Click an icon for replying or forwarding, in the toolbar.

• Select an email draft. Click on Edit draft or on Edit copy in the toolbar.