So i did the following to switch versions:
i first checked the version y was in with : sudo php -v
then ran this to switch to php 7.2 : sudo rm /etc/alternatives/php; sudo ln -s /usr/bin/php7,2/etc/alternatives/php;
seemed to work cause i repeated the first step and it said i was now working on php 7.2
afterwards y went back again to install magento and got a message that:
[InvalidArgumentException]
Project directory ./ is not empty.
i went back again to check and delete any files on the cd /var/www/html and left it this way but it still wont work it keeps trowing the project directory is not empty message.
magento@ubuntu-florentino : /var/www/html $ ls -la
total 12
drwxr-xr-x 3 magento www-data 4096 Jan 27 23:55 .
drwxr-xr-x 3 root root 4096 Jan 27 02:57 ..
drwxr-xr-x 7 magento www-data 4096 Jan 27 22:50 update
magento@ubuntu-florentino : /var/www/html $
Thanks for your help and patience