Yes. If you have the 32 bit version installed, it is recommended that you uninstall the 32bit version, then install the 64bit version. Before you install the 64bit version, backup all your system databases. After the 64bit version is installed stop the SQL Server service, and copy the system database files over the ones that the 64bit installed put in place. You can then restart the SQL Service.
If you are moving from one server to another, then simply detach the databases from the 32bit instance and attach them to the 64bit instance.