Go to installation directory of your copy of Visual Studio
Find VSIXInstaller.exe, usually in location like:
c:\Program Files (x86)\Microsoft Visual Studio <VS-version>\Common7\IDE\VSIXInstaller.exe
run:
VSIXInstaller.exe <full-path-to-downloaded-AlpagExtension.vsix>
From list of available Visual Studio installations choose the ones you want to add the extension to.
If you have multiple installations of Visual Studio, the VSIXInstaller.exe that comes with one Visual Studio may detect other installations, but it is not guaranteed. It is best if you run the copy of VSIXInstaller.exe from the exact catalog of Visual Studio installation you want to add the extension to.
With newer versions of Visual Studio you may get message, that the extension is not compatible with them and may cause Visual Studio to be unstable. Just ignore this message and carry on with installation.
Check:
Start Visual Studio and go to
Tools > Extension manager...
(or Tools > Extensions and Updates... or
Extensions > Manage Extensions - depends on version of VS)
Check if Alpag Extension is listed.
Double check:
Create empty file with .alp extension.
Open it in Visual Studio, type at the start of line a percent sign % or double-percent %%.
Hit Ctrl+Space for contextual help on available directives.
Choose one from available options, like %%ldefs, and check if it gets syntax highlighting.
Notes:
After you install the extension you can delete source AlpagExtension.vsix file, since Visual Studio makes own copy of it.
Installed Visual Studio extension files, can be usually found in location like:
c:\Users\<login-name>\AppData\Local\Microsoft\VisualStudio\<VS-version>\Extensions\
Start Visual Studio
Go to Tools > Extension Manager... (see above for other possible locations of this menu item)
On list of installed extensions find 'Alpag Extension'
Press Uninstall.
Repeat above procedure for each installation of Visual Studio.
Uninstall AlpagExtension from Visual Studio
Install new version using VSIXInstaller
Notes: