To be honest vpn is not the easiest solution, because normally your vpn clients don't get an IP on the same segment as your local network, yes it would be private can controlled by you - but normally its a different segment. So if this webserver is locked down to say 192.168.1.0/24 can access, and your vpn clients get 192.168.2.0/24 then you also have to edit the webserver acl. Or sure the vpn client could then remote one of the machines on the 192.168.1.0/24 network -- if local firewall allows it, normally windows firewall limits rdp access to the local segment, etc. Now sure a vpn can be setup that gives the client same IP as the segment local network is, but this really is not the normal sort of setup when the vpn server is at the edge of the network - say the router providing the connectivity, etc.
This is clearly the much better long term solution to provide robust services to your users. But setup is going to be more complicated then say teamviewer or join.me, webex, etc. Which are simple easy ways to just run some software on a local machine - or even the server itself and let the work in that needs to do something. If its a one off and not very common need then these sorts of remote control software would be easier and faster solutions to the problem.
Normally companies of decent size would already have vpn setup, so this must be a smaller setup - and the fact that the poster is even asking the question has me thinking vpn not already in their skill set, etc. So I believe remote control software - many free solutions that can be used even for business use (join.me for example) is a 1 minute setup for even the novice computer user/admin