I just started playing with NOOBS and a question came to my mind. I installed Raspbian, OpenELEC and OSMC on the same SD.
The config didn't ask how I wanted to split the memory for the three OSs and now I wonder if I can give more space to one of those OSs ( OSMC namely )
A way to resize the different partitions on the NOOBS sd card is to use a different sd card and reformat it with the sizes you wish (with limits) and copy the different filesystems in the partitions to the new sd card. As a guide see the procedures in How can I backup my whole SD to an img file usable with Etcher to restore later?.
The NOOBS image is designed to get new users up and running quickly to play with different OS environments but it is extremely limited has no built-in ability to resize partitions. Once you have decided on a preferred OS, longer term, you really should consider migrated away from NOOBS and make a dedicated OS install for your preferred OS. NOOBS "wastes" a lot of space with the other OSes that you ultimately won't use.
As suggested by @nsilent22, I have had some success resizing partitions with gparted which I access using a Ubuntu virtual machine on my Windowz machine.
