Amro,
Use the parameters below. Make sure and draw your walls, as well:
Since this is a replacement of a deployment that is not working, I would go ahead and do a passive site survey with two or more AP-135s at 12db mounted in two or more rooms to determine the actual coverage before you deploy. For large, important jobs, VisualRF can give you an idea of what you need but only a passive site survey will show you exactly how much coverage you will get, especially if you do not know exactly what is in all of the walls.