The Suntour bar end shifters is made up of 2 parts. There is the shifter unit and there is the mounting unit that secures to the internal diameter of the handlebar.
1. Remove the cables from the derailleurs. Next remove the shifter unit from the mounting unit, this is done by using a flat head screwdriver. Put down any washers that you remove in the sequence so that you do not mess up the installation.
2. Once the shifter unit is removed, you should be able to access the allen key bolt that secures it to the handlebars. Loosen but do not remove it completely. There is an expander wedge that grips the internal surface of the handlebars. Once it is loosen use a small hammer to tap the allen bolt to loosen its grip. You should be able to remove it once the wedge is not expanded.
3. To install it back on the bike do the opposite steps that you removed it.