Here's info regarding how to create and edit php.ini file.
1. Enter your cPanel account and press on "File Manager"
2. Click "Go".
3. Go to folder you that contains your scripts or stay in public_html folder if you want to apply rule for all scripts, not specific. Click on "New File" and enter "php.ini" as filename.
4. After file is created (or if it already existed) choose it in file list and click on "Edit".
5. Simply agree.
6. Enter needed rules and press "Save Changes".
Please note, that php.ini file works only for scripts that are located in same folder. If you create php.ini file in folder "one" and your scripts are in folder "two" located under "one", this won't work.
If you want your php.ini file to work for all scripts in all sub-folders, please check this thread:
Load php.ini recursively for all subfolders