best practice for developing on a live DB

Question

Hi,

I have to make adjustments on a webapplication very often.  This app is used for our production and it is important that it's always available (without bugs).
Therefore I need to copy de DB to a Test DB, to develop and key users have a chance to test the new version.

But after the testingphase all changes made on the Test DB (fields added, changed...), I have to make on the Live DB.
Then I have to make sure offcourse that I didn't forget anything.

Is there a better way to do this?
Copy the data form Live DB to the Test DB is not possible because of the ID's that have been added to the Live DB while developping.


Your insights please..
Thx