1. Your ISP limits you to the upload and download speeds specified by the product you subscribed to. Many of the standard products only allow upload speeds of about 100kb/s . If you have something like that, you may need to pay for a better service.
2. If you are getting a lot less than your product allows, you could check if there is a firmware upgrade for your router.
Got fast download but slow upload speeds? Here's a fix.
3. You could split larger files ( e.g. with 7-zip ) and upload one at a time.
7-Zip
4. You could try Filezilla ( free) which supports resume and transfer of large files >4GB
https://filezilla-project.org/client_features.php