If you encountered the same error just like the image above, just follow this instructions.
Steps:
1. Open your cpanel and look for /wp-admin/ folder.
2. Create a file and name it to .user.ini.
3. Copy the codes below and save the file.
max_input_vars = 5000; max_execution_time = 180;
4. Make sure to switch your PHP Version to 5.4.