I have installed libreelec and raspbian on single SD card using NOOBS. Raspbian got 8GB partition and LibreElec about 5GB. OpenElec takes only 256MB so I would like it to be assigned partition no bigger than 1GB and I would like raspbian to fill rest of the space. How can I achive this?
Changing partition sizes on multi-boot systems is risky, but if you must, use a partition editor from your desktop or laptop. I personally favour GParted on Ubuntu.
Another alternative is to wipe the SD card completely and reinstall by specifying the new partition sizes you want, or making the partitions on the SD card ahead of time, again using a partition editor. For this application, I favour fdisk, available on a number of platforms.