To change the values of a lot of PHP parameters, go to Websites → Manage, search for PHP Configuration on the sidebar, and click on it:
Then, select the PHP Options tab. Below the basic options, you are able to define the values of several parameters, like timezone, disabled functions, and limitations: execution time, file uploads, input time, memory limit, and others.
To set a new value for limits, insert the desired value or select it from the drop-down list, if available:
You can only set values that are equal to or lower than your hosting plan's limit. If you set the bigger value, your hosting plan's maximum value will be applied
You can check limitations and other PHP configuration information on the PHP Info page
PHP parameters, missing on this page, can be changed using the .htaccess file