Check the documentation that came with your monitor or Google the model number and visit the manufacturer's support site to obtain a user manual.
Possibly along the (bottom) edge look or feel for several small buttons, possibly next to the power. One should be for a menu - what you're looking for is the OSD section for vertical and horizontal position, some monitors have an auto setting also. Using the menu and the + and - buttons should allow you to position the display properly in the monitor.
Hope this helps.