This feature is available in all editions.
If I incorrectly enter too many hours in Done can I remove them? How can I edit it?
You can back out an erroneous Effort entry by entering a negative number in the Effort column. If you've entered '88' instead of '48' and saved the entry, you can then simply enter a '-88' to back the entry out. Just be sure it's entered in into the same workitem, by the same person, in the same way it was entered.
You will not be able to correct that on graphs/charts because they rely on historical data. We do not allow changes to historical information in this manner as it would compromise data integrity, but with time, those blips in the graphs will just get further and further behind you.
If I incorrectly enter too many hours in To Do can I remove them? How can I edit it?
To Do gets updated with the "now" current value. If someone enters an incorrect To Do value, they should just update the To Do field with the correct value.