In windows 32, there is a limitation of memory. Whereas in 64 bit you can use all the available memory (except that of required by OS). This will help your database to use more memory which will surely increase your performance.
But there are also certain post upgrade issues which might have some bad impact on the performance, so before moving further please go through the following document:
Kindly check the below documents
How To Change Oracle 11g Wordsize from 32-bit to 64-bit. (Doc ID 548978.1)
Moving Between Windows Servers With Different Word Sizes (32-bit to 64-bit). (Doc ID 400535.1) Note.548978.1 How To Change Oracle 11g Word-size from 32-bit to 64-bit. Note.62290.1 Changing between 32-bit and 64-bit Word Size