Currently, there is no way to upgrade the Maria DB version from the GUI, You can refer the below steps to do the same
1. Connect to the server via SSH
2. Disable Plesk access via any domains with this command:
plesk bin admin --disable-access-domain
3. Make sure that the default virtual host (catchall location for unknown virtual hosts) returns 403. The quickest way to do that is to create a .htaccess file:
echo "Deny from all" > /var/www/vhosts/default/htdocs/.htaccess
4. Comment out all lines in the file /etc/httpd/conf.d/welcome.conf.
5. Log into Plesk
6. Make sure that the option "Tools & Settings -> IP Addresses -> xx.xx.xx.xx > Default site" is set to "None"