There are no attachments after upgrade?
Copy files folder from your old Redmine.
You can change the default files location in the Redmine's configuration file or you can use a symlink. LAN or cloud based network storages for attachments are not recommended because of reliability issues.
Configuration:
./config/configuration.yml
# Absolute path to the directory where attachments are stored.
# The default is the 'files' directory in your Redmine instance.
# Your EasyRedmine instance needs to have read/write permission on this directory.
# Examples: attachments_storage_path: /var/www/redmine/files
Troubleshooting:
If you can't open an attachment, see ./log/production.log for common errors:
Cannot send attachment, /var/www/redmine/files/2015/08/150805095407_xxx.PNG does not exist or is unreadable
ENOENT, Permission Denied... etc.