You can modify PHP's upload_max_filesize as per your needs using CloudLinux's PHP Selector in DirectAdmin.
1. Log in to your DirectAdmin account.
2. In the Extra Features section, click on Select PHP version or type Select PHP inSearch for pages. The option will appear. Click on it. 
3.Under the Account Global Settings, go to the Optionstab.
Note: If it shows an error related to the Native PHP version, change to a non-Native PHP version first.
4. Look for upload_max_filesize and click on the drop-down option displayed in front of it. Then choose the appropriate limit as per your requirements.
A message will appear stating that the maximum upload file size has been changed.
You have successfully increased the upload_max_filesize value using the CloudLinux Selector in DirectAdmin.
