You do not say which version of Malwarebytes you currently have, what kind of licence you currently have, or what OS you are running (I'm assuming Windows).
The most recent version of MWB for windows can currently be downloaded here https://forums.malwarebytes.com/topic/208689-malwarebytes-32-now-available/ you can run the installer over an existing installation.
Older non-expiring licenses are grandfathered into the new versions, or if you are on the newer subscriptions they will of course work.
If you are running MWB v2.2 or earlier , MWB will stop supporting it soon so you have little choice but to upgrade. Earlier teething issues with MWB v3 are largely resolved but as the V3 product is more resource intensive as it protects in more ways - older PCs may struggle.
Lots more info here https://forums.malwarebytes.com/forum/41-malwarebytes-3/
(apologies - missed you were looking for free version - Trial version will revert to free after 14 days)
Edited by x64, 30 September 2017 - 02:33 AM.