Normally you navigate between sheets by using the so-called sheet tab, it sits on the bottom left corner (or right corner, if your sheet is right-to-left). Unfortunately, this might be difficult for low-sighted person as the buttons there are small:
The alternative way is to use the navigational tool bar. This is hidden by default, so go to menu Settings, Toolbars, Navigation and then it will show up:
The buttons in this tool bar can be made large (i.e. in 48 pixels) if necessary.
For mouseless operation, of course this tool bar does not help. But you can use the assigned keyboard shortcut: Ctrl+PageDown for previous sheet and Ctrl+PageUp for next sheet.