He wants to know how to update the version of DOSBox or ScummVM in the games that use them.
For DOSBox: Download the latest version, point the installer at your C:\Program Files (x86)\GOG.com\GAME/DOSBOX directory (where GAME is whichever one you want) and install. When updating to an official version of DOSBox, there shouldn't be too many problems. If you want to use a custom build, expect problems. Either way, back stuff up.
For SCUMMVM: I don't have any of those installed at the moment, but I imagine it is the same basic principle as above, although I would suggest getting the "Windows Zipfile" release instead, and just unzipping it into the appropriate directory.
There are better ways for both, but this should get you started.