You can actually upgrade the PHP version, you can just install a new one.
Firstly, to be able to install a certain PHP version, in this case, 7.2 you’ll need to add a certain repository to your system
sudo apt-add-repository ppa:ondrej/php
Update the repository index.
sudo apt update
Install PHP 7.4 with the below command.
sudo apt install -y php7.4 php7.4-cli php7.4-common php7.4-fpm
To install extensions run
sudo apt install -y php7.4-mysql php7.4-dom php7.4-simplexml php7.4-ssh2 php7.4-xml php7.4-xmlreader php7.4-curl php7.4-exif php7.4-ftp php7.4-gd php7.4-iconv php7.4-imagick php7.4-json php7.4-mbstring php7.4-posix php7.4-sockets php7.4-tokenizer
The above are the required extensions for your WordPRess installation. Having said that it’s good to have these extensions as well.
sudo apt install -y php7.4-mysqli php7.4-pdo php7.4-sqlite3 php7.4-ctype php7.4-fileinfo php7.4-zip php7.4-exif
That’s it, you now have your PHP version installed.