Open up your resource script, either using a GUI editor if you have one, or in a text editor if you don't. Find the static control you wish to modify the text of and give it an id which you should give a numeric value (ie #define it) in your resource header.
Now that the static control has a unique id you can use GetDlgItem to get the handle of the control for use with SetWindowText or just use SetDlgItemText.
eg in resource header:
and then in the resource script:
#define IDC_MY_STATIC_CNTRL 500
Hope that helps.
LTEXT "original static cntrl text", IDC_MY_STATIC_CNTRL, 0, 0, 200, 15