Change Apache default port to a custom port on Ubuntu or Debian

1. Change Apache port 

Edit  /etc/apache2/ports.conf file,

sudo nano ports.conf 

Find the following line:

Listen 80 

Change for example 90

Additionally, change the port number also in 000-default.conf

sudo nano /etc/apache2/sites-enabled/000-default.conf

sudo systemctl restart apache2

and try

http://IP-address:90