How to remove old version of installed snaps

Here's a short script which will remove all old versions of snaps. This will only keep the current active version, which should recover you some disk space:

#!/bin/bash
# Removes old revisions of snaps
# CLOSE ALL SNAPS BEFORE RUNNING THIS
set -eu

LANG=C snap list --all | awk '/disabled/{print $1, $3}' |
    while read snapname revision; do
        snap remove "$snapname" --revision="$revision"
    done

Starting from snap v2.34 and later, you can set the maximum number of snap revisions stored for each package by setting the refresh.retain option—it can only be a number between 2 and 20 and has a default value of 3.

sudo snap set system refresh.retain=2 

A version of the script from another answer, as a one-liner, without the awk dependency:

# snap list --all | while read snapname ver rev trk pub notes; do if [[ $notes = *disabled* ]]; then snap remove "$snapname" --revision="$rev"; fi; done

This likely requires bash or a compatible shell with the [[ construct.