How to control the speed of widget if we set the position in y direction

Well, that widget may not transferred as you would think. It may simply redrawn in the new position. To make an object looks like it is moving, you need to make a loop that looks like something like this:
 

movement_speed = 10; // in milliseconds
old_y_position = 0;
new_y_position = 200;
 
for( ; old_y_position <= new_y_position ; old_y_position++ ) {
    Sleep(movement_speed);
    mtitlebar->SetPositionY(old_y_position);
}

For a correct single threaded solution you should use SetTimer()[^], KillTimer()[^], and WM_TIMER[^]. Here is an example on how to do that: http://msdn.microsoft.com/en-us/library/windows/desktop/ms644901%28v=vs.85%29.aspx#creating_timer[^].
 
About WM_TIMER in a few words: You set up a timer for your window and then you will receive WM_TIMER messages periodially so you can update your animation lets say "10" or whatever times in a second without freezing your gui. Note that you shouldn't expect better then 10ms granularity from WM_TIMER (at most 100 ticks a second) but this is true for a lot of other windows functions too (like the famouse GetTickCount()) and 10ms (and even less) should be quite enough for a smooth animation.
 
EDIT: Don't use blocking calls like Sleep() on your gui thread because that makes your whole gui unresponsive!

You need to create a new thread to change the y direction. Call Sleep() in main thread is not effective.
I want to give you an eg.. But I do not know the type of the "mtitlebar".