You can diminish the size of the journal by means of these commands:

sudo journalctl –vacuum-size=100M

This will retain the most recent 100M of data.

sudo journalctl –vacuum-time=10d

will delete everything but the last 10 days.

The above commands are only temporary

To permanently adjust the size, activate the SystemMaxUse= option there, e.g. as SystemMaxUse=100M to only use 100 MB.

After editing, use service systemd-journald restart to activate the changed configuration. This will remove the excess logs.