Yes: delete all the partitions that you do not need anymore and enlarge the
partitions adjacent to them (in particular those containing data; the system
does *not* require hundreds of GB). Most home users want two partitions on
the internal drive(s): one for the system (tens of GB), whose filesystem
(Trisquel's default, ext4, is reasonable) is mounted on /, and one for the
user data (all the remaining space), whose filesystem (Trisquel's default,
XFS, is reasonable) is mounted on /home. An external drive for backups
(e.g., using the eponymous tool in the "System Settings") is good, although a
backup in a remote location is safer. Maybe one more external drive to
easily share data among systems (e.g., with friends), hence a NTFS filesystem
if some of those systems may be Windows. By the way: you want to backup the
user data before altering the partitions! Everybody should be obsessed with
having backups of the user data. In contrast, having several systems (or
backups of the system) is not much necessary: even if you totally screw the
system up, you can reinstall it in a matter of hours.
You always run the same system, right? If so, why keeping the other systems?
It is only a waste of disk space. If you want, for safety, to keep the
*one* system you currently use and install Trisquel 8 alongside it, you can.
But after some time (which needs not be months), you can delete that older
system as well, to regain the disk space it occupies.
