Yes, of course, you can use gparted
. But the problem is that you can not edit a partition when it is mounted so you have to make a usb startup disk first (using e.g. startup disk creator which is also called usb-creator-gtk
). If your computer has access to a DVD drive you can burn the ubuntu disk image onto a DVD as well.
When you started the computer with the live disk, open a terminal and enter
sudo gparted
When prompted for password, just press enter and then you can edit the partition table.
One general hint (which may not be applicable to your situation) is that it takes much less time if the new partition you create, lies at the end of the original partition and not the beginning (because otherwise gparted has to move all the original partition bit-by-bit). So, just resize the original partition and do not move it, otherwise the job can take a few hours.
If you want, you may be able to recover your windows partition using testdisk (before repartitioning of course).