As new versions of php are being released, the following are the steps to upgrade your php version on ubuntu.
Step 1
Step 1 involves updating your box and installing a few packages with these commands
sudo apt-get update
sudo apt -y install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
Step 2 : install php 7.4
sudo apt -y install php7.4
Step 3 Configure php7.4
On apache
sudo nano /etc/php/7.4/apache2/php.ini
On nginx
sudo nano /etc/php/7.4/fpm/php.ini
a few preferences changeable settings in your php.ini file
upload_max_filesize = 32M
post_max_size = 48M
memory_limit = 256M
max_execution_time = 600
max_input_vars = 3000
max_input_time = 1000