Leave only 3 days log records on server:
journalctl --vacuum-time=3d

Deleted archived journal /var/log/journal/97dbaa8c02f24706aae95a937e75f70c/system@d30241f66d70465d8cbe2b3992364ea0-0000000001d37cce-00057cddd384d48c.journal (120.0M).
Deleted archived journal /var/log/journal/97dbaa8c02f24706aae95a937e75f70c/system@d30241f66d70465d8cbe2b3992364ea0-0000000001d55995-00057cee2834a5a3.journal (120.0M).
Deleted archived journal /var/log/journal/97dbaa8c02f24706aae95a937e75f70c/system@d30241f66d70465d8cbe2b3992364ea0-0000000001d740d2-00057cfe270c1c83.journal (112.0M).
Deleted archived journal /var/log/journal/97dbaa8c02f24706aae95a937e75f70c/system@d30241f66d70465d8cbe2b3992364ea0-0000000001d915e8-00057d0eaa2713ee.journal (120.0M).
Deleted archived journal /var/log/journal/97dbaa8c02f24706aae95a937e75f70c/system@d30241f66d70465d8cbe2b3992364ea0-0000000001daf769-00057d1f2d5560e2.journal (112.0M).

…

Leave only last 100MB data on server:
journalctl --vacuum-size=100M