After some weeks of use, /dev/root is full

Hi,
after some weeks of pi-hole use on my raspberry pi (1st version) I have found that it was impossible to update my raspian through "sudo apt-get update && sudo apt-get upgrade" because the space is full.
Infact, I have comfirmed that the space is full (100%) with "df -h".
Is it normal with pi-hole? How can I resolve this issue? I would clean /dev/root
thanks

You can gain some space with sudo apt-get -y clean command

Thanks, but this command doesn't increase the free space.
I try to remove wolfram-alpha and now the free space is about 10%.
Infact, now:
"df -h"

pi@raspberrypi ~ $ df -h
File system                 Dim. Usati Dispon. Uso% Montato su
/dev/root                   3,6G  3,1G    353M  90% /
devtmpfs                    103M     0    103M   0% /dev
tmpfs                       107M     0    107M   0% /dev/shm
tmpfs                       107M  8,5M     98M   8% /run
tmpfs                       5,0M  4,0K    5,0M   1% /run/lock
tmpfs                       107M     0    107M   0% /sys/fs/cgroup
/dev/mmcblk0p1               56M   21M     36M  37% /boot
tmpfs                        22M     0     22M   0% /run/user/106
tmpfs                        22M     0     22M   0% /run/user/1000
pi@raspberrypi ~ $

is it possible?

A 4 Gig card running full Raspbian is very small. The recommendation is for 8 Gigs or larger. If you are limited to which card you can use, I would suggest giving Raspbian Jessie Lite a try. It's headless, meaning no desktop environment, but should give you some space to work with. (The packages that seem to take up a lot of room are Wolfram, NodeRed/NodeJS and the desktop environments.)

Or just add a USB thumb drive, copy all files on the SD cart to the USB drive except for the "boot" folder. then configure the file system to use the USB drive for all directories except for the /boot witch will have to be on the SD card. You will find plenty tutorials on the web about how to do this. This way you can use any sd card larger than 50 mb.