@jasssjj555 You really shouldn't have to upload any WordPress core files from your local host. So I'm not sure what files you are having trouble replacing.
Once you have a fresh WordPress install it is just matter of FTPing your theme folder (wp-content > themes) onto the server then importing your site's XML file. Tools > Export then in the new intall Tools > Import. You can easily reinstall any plugins in the dashboard.
@jasssjj555 Hmmm... Could it be you are uploading the wrong file? Some theme zips (which are gargantuan in size and include documentation/tutorials, etc.) have to be opened/extracted to get to the actual core theme files zip which is a much smaller file.
Check that out... HTH! 😉
Judith "You have to be odd to be number one." Dr. Seuss