By minimising the map you decrease its size. In order to minimise the map, you must first have maximised it. If you have not done that, you can disregard the information in this section.
To minimise the map:
Go to the map (see image below).
Click "Minimise" (see the first image below). When you do so, the map will be minimised, meaning it will regain its original size (see the second image below). The original size depends on whether you are showing both the map and the KPIs, or only the map.