Fedora did a thing I hated in Windows. It collected enough system files to flood my root partition over the years of usage.

[root@hp ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
rootfs                 15G   14G  403M  98% /
udev                  996M  316K  996M   1% /dev
tmpfs                1004M  1.5M 1003M   1% /dev/shm
/dev/sda2              15G   14G  403M  98% /
/dev/sda1             485M  166M  294M  37% /boot
/dev/mapper/luks-6e55a54f-c3c6-45d9-99d3-a6d8015b2baa
                       97G   16G   76G  18% /home
/dev/sda6             117G  105G  5.9G  95% /home/t1/media

Top space consumers are:

[root@hp ~]# du -sh /*
156M    /boot
370M    /lib
7.3G    /usr
5.3G    /var
[root@hp ~]#  du -sh /usr/*
550M    /usr/bin
1.2G    /usr/lib
1.9G    /usr/lib64
3.4G    /usr/share
[root@hp ~]# du -sh /var/*
3.9G    /var/cache
890M    /var/lib
407M    /var/spool
[root@hp ~]# du -sh /var/cache/*
1.1G    /var/cache/abrt-di
2.8G    /var/cache/yum

A workaround:

[root@hp ~]# rm -rf /var/spool/abrt/*
[root@hp ~]# rm -rf /var/cache/abrt-di/usr/lib/debug/.build-id/*
[root@hp ~]# rm -rf /var/cache/yum/*
[root@hp ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
rootfs                 15G  9.3G  4.5G  68% /

Enough for preupgrade now!