After spending two minutes clicking around my free account, I couldn't see either how I'd upgrade to a paid account or why I'd want to. Seems like an important usability issue.
On GitLab.com? We're not offering paid upgrades there (you can only pay for support, $9.99 p/u/year [0].
Most of our customers run GitLab on their own servers, for which you have to pay if you want to run Enterprise Edition. You'd be prompted for a license key and the means to get one.
It might be a good idea to do this differently in the future, but we're not keen on running anything else than default GitLab EE on GitLab.com.
There are FOSS projects that would like to host with you but won't because "Take advantage of all the benefits of GitLab EE" is a requirement on gitlab.com instead of something you can elect to use.
I'm not one of those people, by the way, but I do understand the frustration of seeing someone handing out cheese and crackers, and after stepping up to ask for "no cheese, thanks", being told they must take it with cheese.
We understand the dilemma. For us it is important to be able to run all the EE features at scale so we can troubleshoot problems on an environment we have access to. You can use GitLab.com without using the EE features, but you can't disable the features. We thought about disabling or marking the features but this seemed too complex. For a list of the differences please see https://about.gitlab.com/features/#compare
Most of our customers run GitLab on their own servers, for which you have to pay if you want to run Enterprise Edition. You'd be prompted for a license key and the means to get one.
It might be a good idea to do this differently in the future, but we're not keen on running anything else than default GitLab EE on GitLab.com.
[0]: https://about.gitlab.com/gitlab-com/