Is my Ubuntu installation full? An app said my disk was full on Xubuntu 18.04

Trying to download an engineering program, Salome-9.4.0, of size 2 GB. The download stopped right about when it was 99 or 100% done as it "ran out of disk space". It was downloading to my Desktop on my Xubuntu 18.04 system. Xubuntu uses the XFCE desktop rather than the older Gnome.

My laptop has 2 drives and is dual boot (Win-10 + Xubuntu 18.04). The smaller SSHD boot drive appears to have used 64 of 128 GB. The 2 GB data drive (also an SDD) should be < 25% full. Maybe this is 2 TB? It's a big modern drive.

df returns the following info:

jim@Zenoba-Lin:~$ df
Filesystem     1K-blocks     Used Available Use% Mounted on
udev             6084632        0   6084632   0% /dev
tmpfs            1221408     1484   1219924   1% /run
/dev/sda6       15198088 14190588    215744  99% /
tmpfs            6107028   372608   5734420   7% /dev/shm
tmpfs               5120        4      5116   1% /run/lock
tmpfs            6107028        0   6107028   0% /sys/fs/cgroup
/dev/loop0         56320    56320         0 100% /snap/core18/1705
/dev/loop1         56064    56064         0 100% /snap/core18/1668
/dev/loop2         27776    27776         0 100% /snap/snapd/6953
/dev/loop3         63616    63616         0 100% /snap/gtk-common-themes/1506
/dev/loop4         56192    56192         0 100% /snap/gtk-common-themes/1502
/dev/loop5          7936     7936         0 100% /snap/gedit/371
/dev/loop6         27776    27776         0 100% /snap/snapd/7264
/dev/loop7         18432    18432         0 100% /snap/gedit/537
/dev/loop8        164096   164096         0 100% /snap/gnome-3-28-1804/116
tmpfs            1221404       24   1221380   1% /run/user/1000
/dev/sda1       95506172 75104356  20401816  79% /media/jim/SSHD_boot

Does this mean my Ubuntu installation is filled up? Is there a way to adjust partitions so as to get more space? Eventually I may buy a bigger boot flash drive than the 128 GB.