Hi,
You can upgrade your WOrdPress manually. Below are the steps.
1. Download the latest WordpPress zip file and unzip that file.
2. Deactivate plugins.
3. Delete the old wp-includes and wp-admin folder and upload the new wp-includes and wp-admin folders.
4. Do NOT delete your existing wp-content folder just Upload the individual files from the new wp-content folder to your existing wp-content folder, overwriting existing files.
5. Upload all new loose files from the root directory of the new version to your existing wordpress root directory.
6. Don’t do any changes in wp-config.php file.