If you’re on Windows, try holding down the Ctrl key while turning the scroll-wheel on your mouse. (If you don’t have a mouse, hold down Ctrl while doing whatever you usually do on your laptop to scroll up or down. On some laptops, the right-most strip of the touchpad acts as a virtual scroll-wheel. On others, a two- or three-finger gesture anywhere on the touchpad causes scrolling.)
If you’re not on Windows, there may be a similar scroll-to-zoom feature; Google around for it, or try looking under your Accessibility menu to see if there’s anything listed there for magnifying/reducing the screen or the text size.
Horizontal real-estate has always been a challenge in Manager, largely due to the amount of horizontal space the left-side menu occupies. @Lubos has recently implemented “Compact Mode,” allowing the menu to auto-hide, which frees up some horizontal real-estate when it is invoked.