The best way is to use the "fix it" in this tip:
http://support.microsoft.com/kb/2739501
Office 2013, Office 365 and Office 2013 Preview uninstalls
PS: exactly why do you want 64-bit Office. MS Still recommends most people use 32 bit Office, even on 64 bit Windows.
Optional Reading
Why can’t I install both the 32-bit and 64-bit versions of Office 2013?
http://office.microsoft.com/en-us/access-help/why-cant-i-install-both-the-32-bit-and-64-bit-versions-of-office-2013-HA103523746.aspx
Blocking and nonblocking Office applications in 64-bit installations
If 32-bit Office applications are installed on a computer, a 64-bit Office 2010 installation is blocked by default. The following section (Applications that
block a 64-bit Office 2010 installation) lists the applications that block a 64-bit Office 2010 installation. The next section (Applications that do not
block a 64-bit Office 2010 installation) lists exceptions; that is, applications that do not block the installation. In such cases, installation of 64-bit Office proceeds even if the listed 32-bit applications are installed on the computer.
Applications that block a 64-bit Office 2010 installation
The following applications block a 64-bit Office 2010 installation:
- Microsoft Office Excel Viewer
- Access database engine of Microsoft Access 2010
- Microsoft Office 2010 (Click-to-run)
- Compatibility Pack for the 2007 Office system
Applications that do not block a 64-bit Office 2010 installation
The following applications do not block a 64-bit Office 2010 installation:
- Microsoft Visual Studio Web Authoring Component 2007
- 2007 Microsoft Office system 64-bit components
- Microsoft Office 2010 (OEM pre-installation)
- Microsoft Office 2003 Web Components
- Expressions Web Designer
- Microsoft Office XP Web Components
- Microsoft Expression Web 1
- Microsoft Expression Web 1 Language Packs
- Microsoft Expression Web 2
- Microsoft Expression Web 2 Language Packs
- Visual Basic for Applications 6.4 SDK
- Visual Basic for Applications 6.4 SDK International Components
“This 64-bit product may not be installed with Microsoft Office Click-to-Run” Error message when you try to install a 64-bit version of Office
http://support.microsoft.com/kb/982258