There is no such thing as float:center; in CSS. You can use either text-align:center; on the containing element or margin:0 auto; on the logo element itself.
Make sure you are uploading the files in the proper transfer method, for example files like PHP, CSS, etc. which are readable should be uploaded in ASCII, but files like gif, jpg, png, or any other files that aren’t text characters should be uploaded in BINARY. I’m not sure about Filezilla as I never use it but usually they do this automatically these days unless you have a setting changes somewhere I think.
It may also be normal for the file size to be slightly different since it may be a different OS with a different file system. If you can open the file on the server and it’s all there then there should be nothing to worry about.