File/attachment size limit isn't a configurable option in HipChat Server admin interface at the moment however you are welcome to vote up the public feature request about this matter here: HCPUB-374. There's a user who shared a workaround for that however it may work only on web client since there's a hardcoded limitation enforced on the desktop client.
...from the beginning. We have built up a lot of content in HipChat, with it being a core tool in our distributed company model. While it is true that we didn’t need to move to Slack immediately, we felt it...
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