the paypal code is added to the checkout.php, confirm.php and pp_confirm.php page bu the checkout wizard.
on those pages look for code siomilar to:
$WA_PP_ECO_Set_params[0][$nextIndex] = "UseSandbox";
$WA_PP_ECO_Set_params[1][$nextIndex] = "true";
and change it to false.
also on those pages, the code that passes the API Username, password and Signature will need to be changed to use the live api info, it will look similar to:
$WA_PP_ECO_Set_params[0][$nextIndex] = "Username";
$WA_PP_ECO_Set_params[1][$nextIndex] = "<api user>";
$nextIndex = count($WA_PP_ECO_Set_params[0]);
$WA_PP_ECO_Set_params[0][$nextIndex] = "Password";
$WA_PP_ECO_Set_params[1][$nextIndex] = "<api pass>";
$nextIndex = count($WA_PP_ECO_Set_params[0]);
$WA_PP_ECO_Set_params[0][$nextIndex] = "Signature";
$WA_PP_ECO_Set_params[1][$nextIndex] = "<api sig>";
on the pp+confirm page, there will also be another line to change:
$WA_PP_ECO_GetResult = WA_PP_ECO_Get_Post("<api user>", "<api pass>", "<api sig>", "true");
the api info needs to change and the final true needs to change to false:
$WA_PP_ECO_GetResult = WA_PP_ECO_Get_Post("<api user>", "<api pass>", "<api sig>", "false");