Convert CMS from SOLO version to PRO I've had to continue with a Craft CMS install somebody else did, now trying to make sense of it.

A client bought a PRO licence, but the CMS seems to still have a SOLO installed. Is there anyway to convert one to another without having down time in the site?

There is no option to upgrade the CMS once you bought the PRO license.

Thanks in advance

Edit: worth noting that clicking "reactivate" results in a "Craft has successfully been upgraded" but does not result in the removal of the "trial" message in the bottom or in added functions.
“Reactivate” is the button you are looking for. Try checking for updates so Craft gets updated license info – the Trial badge sholud go away once Craft realizes that it’s licensed to run Pro. (If not, please contact support@craftcms.com and send in your config/license.key file, and we’ll sort it out.)