Unfortunately, the URL slug cannot be changed because it causes a lot of cascading breakage throughout the rest of the community. 😔
However, you can switch to a custom domain which will hide the URL slug entirely. Here's a quick guide on how to do that: https://guide.heartbeat.chat/custom-domains
Or if you have an AppSumo license, you can create a new community here, and then reach out to support to let us know the community name, and we can transfer the license to the new community.