I had previously installed windows 8.1 on my hard drive, then I later unallocated some space like 15GB and installed linuxmint separately on that partition, How to extend the 15GB volume that I have allocated for linuxmint without any loss of data?
To assume you have enough space of the win 8.1 install:
1) boot into (or use a install cd) for windows and shrink its partition to the desired extension size then boot into a mint install cd/usb
(DO NOT ATTEMPT FROM INSTALLED MINT)
2) mount and "chroot" the mint install (which has both fdisk / gparted -- for newer users gparted is hands down safer option --its also gui based.
3) then extend the 15Gb mint install by the newly re-un-allocated space and click apply.
4) then from mint installer -- open a terminal (Clt-Alt-F2 by default) and run:
sudo update-initramfs -u -k all && sudo update-grub
(FOR THIS ENSURE YOU ARE IN THE "CHROOT" --change(d) root) -- can confirm by running lsblk (which should NOT show /mnt/...... only native /, /home,etc etc.
5) exit the "chroot" via Clt_d or typing exit TWICE)
6) reboot --removing install media prior to restart
7) enjoy newly enlarged mint install on your dual booted system.