Hi,
Your theme is using the same function name as one of WordPress' core functions.
To fix this you'll either have to manually edit your theme files, or change to a default theme until an update is available for the theme you are using.
To manually edit the theme, you will have to edit the file in 11_other.php found in wp-content/themes/prestige/, on line 99 it should say function the_post_thumbnail_caption() {, you will have to remove this up to the closing } (they come in pairs).
Alternatively, to switch to a default theme, you will have to use an FTP client, or your hosts File Manager tool to change the name of the prestige folder found in wp-content/themes/ to something else (personally I just add .old to the end of the folder name), this will make WordPress use a default theme instead.