If you did not follow standard installation instructions and installed the mail server into
the folder other than default c:\Program Files (x86)\, then you can just install the 64 version normally, the similar way
you would do an usual upgrade.
It also would be safe to install the 64-bit version into the same x86 folder, but probably, it is "nicer" to follow
"rules" and keep 64-bit applications in the Program Files folder, rather than in x86 folder.
First, uninstall the 32-bit version from the Uninstall or Change a Program
applet in the Control Panel. When prompted
if you are upgrading to new version, answer YES.
Then, if you are using SQL version, run SQL Server Management studio and
detach MailServerData database from SQL server. If you are using SQLite,
then you can skip this step.
Then locate the file Settings.xml (instructions how to locate it are below in
this FAQ), open it using Notepad (OK, you may will need to move it to desktop,
and edit it there, and save it and copy it to its original location, sometimes
there are some user access rights problems). Go through the Settings.xml
file, and wherever you see references to folder c:\Program Files (x86)\ change it
to just c:\Program Files\.
After that, move the entire content of C:\Program Files (x86)\ArGo Software Design\ArGoSoft Mail Server .NET
to C:\Program Files\ArGo Software Design\ArGoSoft Mail Server .NET.
Using SQL Server Management studio reattach the MailServerData.mdf file to the SQL server as MailServerData.
No need of doing that if you are using SQLite.
Install the 64-bit version of mail server into the standard folder C:\Program Files\ArGo Software Design\ArGoSoft Mail Server .NET.