Home Page Bug

this piece of code appeared on the front page

What piece of code?

“Notice: Trying to get property of non-object in /hermes/waloraweb005/b161/moo.aretehoopscom/wp-includes/post-template.php on line 29”

Try:
– switching to the default theme by renaming your current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using FTP or whatever file management application your host provides.

– resetting the plugins folder by FTP or phpMyAdmin.

– re-uploading all files & folders – except the wp-content folder and the wp-config.php & root .htaccess files – from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.

– running the upgrade manually via wp-admin/upgrade.php

If I switched to the default theme would my changes in child theme be erased?

i tried resetting the plugins folder and that didn’t work and I’m not sure how to re-upload all files and folders…Would I have to do that through my hosts website? Or could I do it manually through FTP?

Thanks