If you plan to edit the entire hub, you will first click on the main "edit" button at the left top of the screen. Then you will have to click on "edit" for each hub module in order to make changes or delete entirely. If you want to add something, click on the appropriate designation (text, photo, poll, link, etc.) found at the top right of your edit mode screen, then work on that new module.
Do you have the best title possible? If not, try for a better one. Does your summary succinctly state the essence of the hub's material? If not, improve it. A good summary can give you a reader who might pass the title by with little interest.
If you're referring to copy editing an existing hub, first read it in entirety, beginning with the category you assigned it to when first published. I suggest more than one read-through, with the first dedicated to proof-reading, finding and correcting any errors in structure, facts, grammar, etc. to make your hub more readable.
Then, if anything in your hub needs updating to make it more relevant to present-day readers, make those changes. If you think adding new graphics, music, videos or photos will add to the overall quality of the hub, do that now.
Read it through one more time to get a feel for what readers who click on your title find once that hub is onscreen. If you're satisfied with what you read, click on the button that means you're finished editing and ready for it to be online again.
No matter how many hubs you have published on HP, you should do "preventive maintenance" on each of them periodically. Set up a schedule to review a few (five? ten?) each week and edit as needed until you've worked your way through the entire lot. Hubs intended to be evergreen and continue attracting readers should get your first attention.
As Hubbers, we can't rest on our laurels. While writing and publishing new hubs should be our goal, we need to ensure that existing hubs are always the best that they can be. Reviewing them on a schedule and editing (as needed to improve) is the way to do that.