Files such as images that are uploaded in SlimWiki are stored in Amazon S3 which has many regions around the world. 

Non-US locations may result in better performance for teams located outside North America. 

Previously uploaded files will remain in their original location prior to you changing this setting.

1) Navigate to Account Settings

2) Select the closest file storage location to your current location from the drop-down list of locations

3) Click 'Save' after selecting the location