No, you don't. There is no difference in behaviour between a 32‑bit and a 64‑bit JDK. You will have to reinstall Java™ anyway, because there is a new update, and you will find all the downloads here. Including the 32‑bit versions.
The "Windows x86" version is the 32-bit version. It can be installed on 32-bit and 64-bit Windows.
The "Windows x64" version is the 64-bit version. It can be installed only on 64-bit Windows.
You can have the 32-bit and 64-bit versions installed at the same time, as long as you install them in different directories. However, why would you want this? Note that Java bytecode is independent of the "bitness" of the JVM and operating system - you do not need to compile your Java program with the 32-bit and 64-bit versions separately, there will be no difference at all in class files that are produced, and classes compiled with the 32-bit version will run on the 64-bit version and vice versa.
There is no difference in behaviour between a 32‑bit and a 64‑bit JDK
Difference in memory consuming 64 bit JVM consume more memory than 32 and therefore you application consume more, recommendation is to have at least 15% more memory if you want to use 64 bit java instead of 32.
May the force be with you!
subject: how to install jdk32 bit on a windows7 64bit machine