Resizing existing partitions on an external USB2 HDD in Mac OS?

Hello.

Mac OS (Mountain Lion v10.8.5 & Sierra v10.12.1)'s Disk Utility won't
let me resize 2 existing partitions (FAT32 [datas and sharing with other
OSes like Windows] & encrypted HFS+ [Time Machine + other datas]). I
wanted to make its FAT32 partition smaller & HFS+ partition bigger
without losing data, redoing from scratch, etc. It doesn't seem to let
me. Does its Disk Utility not let me do that like in Linux and Windows?


Thank you in advance.
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