To Edit a constant, you must first know the Constant group containing the constante (You can use the Find Object item of the Edit menu).
Normly, you should have this type of window displayed on the screen:
Then, you can edit the constante.
There are 6things that the ser can modify on a constante:
The Valst value Label give you the value assign to the constant the last time it was calculated.
In this window, you can use the arrow to navigate thru the edit boxes.
Pressing ENTER key when writing the name of a new constant will create it and place the focus on the valu dialog box of this constante.
Pressing simultenely the Ctrl key and up or down allows you to modify the position of a constante. This is not realy important in normal mode, but it can be usefull when using autocalculated constante (See Constantes for more explainations).