Hi, is there a way to change the logo in the application?

Can I use this instead of Cloudinary ?

OwnCloud and Cloudinary doesn't really have the same goals, Cloudinary is more about media-management (like image optimization and such) while OwnCloud is more about just general purpose file storage with an emphasis on security. Since OwnCloud is general purpose file-sharing you could theoretically use it instead of Cloudinary but whether it makes sense to use OwnCloud over Cloudinary will depend on your preferences and use-cases