3CX 2SC STD v 20

[Yolande AppTech]

We have a client on the free 3CX 2SC STD version 20 - but I seem to recall they used to have 4SC ability - not sure if this changed with the version update? If they do not want to opt for upgrading to the paid 4SC Pro version - what other options do they have and how do I get this changed back to the 4SC again? How many simultaneous calls can be made on the 3XC SME free version and can they upgrade to this?