Not sure what you mean by "upgrade" so this is how we see it.
1. We have member ranks. Registered members, Verified members, Uploaders, and Power users. To move from one rank to the next we call it promotion and not upgrade. Ranks are merit-based and they cant be "bought".
2. We call upgrade when one becomes VIP or Donor. Those receive special perks that you can find here:
You must be registered for see links
Those are paid of course.
Now why we dont allow just anyone to upload torrents? Mostly security and quality. This community is built around trust and user interaction. We dont want just people popping and uploading any torrent they find on the net without knowing who they are and what they are uploading. Is it secure? Is it working? Will the uploader be there to support its uploads and help members? Those are more crucial to us than just becoming another torrent site like the thousands out there.
Do we always succeed on members or the quality of uploads??? No, but we can say that we tried. Most of our uploaders are long-term members often dedicated to helping and also making sure what they upload is as safe as it can be because of the nature of the site (software). You cant catch a virus with movies or mp3s but it's really easy for someone to spread viruses etc if they are unchecked.
That is why our requirements are mostly based on interaction. No of posts and comments, No of likes, etc. We still give an option to registered users to upload via direct links and start building their "name and reputation" but we reserve torrents for those who want to go the extra mile with us.
Hope you understand.