If you are going to upgrade MailBee.NET Objects and dowloaded package installer MailBeeNetObjects.msi, the first thing to do is to close all applications which are using MailBee.NET. If Visual Studio .NET is running, please close it too. After that, you need to remove previous installed MailBee.NET components package. To remove existing version of the product, use Add/Remove Programs in the Control Panel. Then, new version of MailBee.NET can be easily installed – just run installer and choose path for the program.
In case if you have downloaded only a new version of MailBee.NET.dll, the first step is the same: close all applications which are using MailBee.NET. After that, you should manually replace old MailBee.NET.dll file in installation folder (such as C:\Program Files\MailBee.NET Objects) and in Global Assembly Cache (such as C:\Windows\assembly, you should use Windows Explorer to overwrite MailBee.NET assembly).
For Visual Studio.NET, in both cases you don’t need to change anything in your projects (assumed that you referenced MailBee.NET Objects library as it shown in Documentation).
For non-Visual Studio.NET environment you should manually replace MailBee.NET.dll file in the /bin subfolder of your application. After installation of MailBee.NET package you can find MailBee.NET.dll file in installation folder (by default it is "C:\Program Files\MailBee.NET Objects").