1.You have to set the Template summary to X64;1033 in Installation Information ->General Information -> Summary information stream. Where 1033 is the language code. If you need more than one language then you give as X64;1033,1031
2. Set the destination for the components to [ProgramFiles64Folder] instead of [ProgramFilesFolder].
3. If you have any 64 bit self registrable dll, then set the component property "64-bit component" to"Yes".
4.In script if you are using any registry related API, then add below two lines of code before and after calling the registry API in code respectively.
//This will cause all subsequent registry operations to access the 64-bit section REGDB_OPTIONS = REGDB_OPTIONS | REGDB_OPTION_WOW64_64KEY; //added for 64 bit support
REGDB_OPTIONS = REGDB_OPTIONS & ~REGDB_OPTION_WOW64_64KEY; //to revert to 32-bit.
