Go to http://www.mikrotik.com/download and select Download archive.
Select from current release tree the 6.36.1 version. Download the all_packages-mipsbe-6.36.1.zip file. Extract the file.
Drag 'n' drop user manager package in Winbox - Files.
Make a reboot.
How many users can handle?
I have 100/30 mbit net line
25 vpn users on rb435g with ap 2,4ghz and 5ghz link to another network
Cpu is high and users cant get net line higher than 10-12mbit
Bandwith test via wifi run 80-120mbit on 5ghz link