You can check how much disk space you are using by running the df command.

root@droplet:~# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vda1        40G  3.9G   34G  11% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
udev            999M  4.0K  999M   1% /dev
tmpfs           202M  324K  202M   1% /run
none            5.0M     0  5.0M   0% /run/lock
none           1008M     0 1008M   0% /run/shm
none            100M     0  100M   0% /run/user

The -h option is used to output human readable sizes (e.g. 34G instead of 34000000000 bytes).

In this example, the droplet is using 3.9 gigabytes of disk space.

You should clean temp and set it's size.