jail.conf is the fail2ban default configuration file. However, if you want to adjust anything, as noted in jail.conf file itself, it is better to create /etc/fail2ban/jail.local and put your adjustments there.

I like to make adjustments as follows,

sudo touch /etc/fail2ban/jail.local
sudo ne /etc/fail2ban/jail.local # using ne to edit the file

Add the following to the file,

# The DEFAULT allows a global definition of the options. They can be override
# in each jail afterwards.

[DEFAULT]

maxretry = 10

For configuration changes to take effect you need to restart the service,

sudo /etc/init.d/fail2ban stop
sudo /etc/init.d/fail2ban start