Is it possible to upgrade a portable Python 32 bit install to a 64 bit install?

No, it is not possible to upgrade a 32bit Python installation to a 64bit one.

Still, there is something that you can do in order to speedup installation of a new 64bit version.

Run pip freeze > packages.txt on the old installation in order to generate a list of all installed packages and their versions.

After you install the new python version, run pip install -r packages.txt in order to install the same version of the packages that you had on the old installation.

As I see you use scipy, you may want to have a look at Anaconda. It could save you a lot of time.

make a backup of you "Lib" folder present in your python installation folder. Now when you install your python 64 bit paste this "Lib" folder there. After this, you don't need to install many modules again.