how to UPDATE a DB?



I have a DB with quite a few fields in it and I can get the info INSERT'ed and I can get it out again as a result, but how do I UPDATE it?

I know how to get the info back into the form EXCEPT for scroll down menues and check boxes, how do I get them to get the result from the DB so the right think is selected in the scroll down menu and so the check box is checked, if it is listed as checked in the DB?

on all normal text fields I just put in value=$varname and that puts the info in just fine and in textfields you just have to put the $varname inbetween the <texfield> and </textfield>

any suggestions on how to do this thing?


***edited in***
I forgot to add, how do you make sure that it writes on top of the old row and doesn't make a new one?
***edited in***
you got a solution to how I get my info from the database into the CHECK BOXES and ROLL DOWN MENUS?

all other I get in nicely but I can't figure out how to enter the state of those two with info from the DB

I couldn't find that link, so I went for the MySQL website instead ;o)