Fatal error: Cannot redeclare uc_order_views_data() After clicking Continue @ /update.php, we receive:

Fatal error: Cannot redeclare uc_order_views_data() (previously
declared in
/home/user/public_html/sites/all/modules/ubercart/uc_order/views/uc_order.views.inc:13) in
/home/user/public_html/sites/all/modules/contrib/ubercart/uc_order/views/uc_order.views.inc
on line 708

When I remove either version of the ubercart directories, the /update.php process complains that the directory is missing.
I can't see a double-up of modules in /admin/modules
The two ubercart directories both contain the same subfolders.
I did not develop the website, but took over maintenance of it.
&quot;When I remove either version ...&quot;
&quot;I can't see a double-up of modules in /admin/modules&quot;
&quot;The two ubercart directories both contain the same subfolders.&quot;
It sounds like you have two copies of Ubercart on your server. THAT IS NOT ALLOWED for ANY Drupal module. You must have one, and only one, copy of each module.
The correct way to update a Drupal module is to completely remove the old version of the module code first, then replace it with the new version of the code. Then you can run update.php.