Increasing Post Maximum Size
To increase the Post Maximum Size do the following:
Step 1: Locate the php.ini file inside the /wp-admin directory using an FTP client or file manager in your web hosting control panel (if you’re not sure how to do this, ignore the steps below and contact your web host who can do this for you).
Step 2: Find the following line in your php.ini file:
Step 3: Increase the value to 64MB or higher and save the file.
Step 4: If you still have issues, look for this file in your root directory and make the same changes.