WordPress have 20 MB media library upload threshold, which is sometime annoyed when you need to upload large numbers of files. Let's suppose if you want to upload 50 MB file so their size or volume is not comply with WordPress upload files threshold, which is 20 MB. Means that, you can not upload those files which size is more than 20 MB. So what that is solution in this situation. Let's see,
Login to your WordPress dashboard and navigate to Plugins > Add New.
Search Add From Server plugin then install and activate in your WordPress.
Now you will upload your file on server "Upload" folder via FTP client, which default path is from WordPress root directory, example:
After done uploading, comeback on WordPress dashboard then navigate to Media > Add From Server. Add From Server shows complete root directory, so then you need to choose that folder in which you drooped your file via FTP client.
After get your file, simply check/select file and finally click on import.
You have successfully import your file in your media library. You can also read how to Upload Large Files in WordPress. That's all.