If you followed my earlier blog How to install and configure pgAdmin4 for FreeBSD and with uWSGI you will see it was written for version 4.6 of pgAdmin4.
Upgrading pgAdmin4 isn't difficult, on fact you only need todo 3 steps to complete the upgrade:
First step, activate the virtual environment
$ source /opt/pgadmin/pgadm_env/bin/activate
Second step, upgrade pgAdmin4
(pgadm_env)$ sudo pip install https://ftp.postgresql.org/pub/pgadmin/pgadmin4/v4.8/pip/pgadmin4-4.8-py2.py3-none-any.whl
Third and last step, restart uwsgi
$ sudo service uwsgi restart
That's it, super simple!