You are entitled to run 32 bit or 64 bit with any Windows 7 license including manufacturer's OEM. However since you have an Upgrade Kit which is specific to the version that came with the machine, I am not sure they will now send you 64 bit to clean install.
However, thanks to MS insistence most of these manufacturer's Upgrade kits have a clean copy DVD of Windows 7 enclosed, along with a drivers
/apps CD which is surprisingly free of bloatware - so far. The Windows 7 Upgrade DVD has a product key which is tied like the Vista OEM to the machine's mobo.
I would call my manufacturer and ask if you can be supplied with the 64 bit install DVD to do a clean install since this can be done with the DVD anyway. They may reveal reasons why your model is not suited for 64 bit. Then I would do my own research, starting with the Windows 7 Upgrade advisor, and decide if it is a worth a try on your own, as follows:
Locate a copy of 64 bit Windows 7 RTM of your version. You can unlock all versions in the RTM by removing the ei.cfg file from Sources, then recompiling and burning the edited ISO: Bootable ISO - Create from Installation Files
Make a Windows 7 backup image of your full HD saved externally so you can easily reimage back to your current installation if necessary.
Boot from the 64 bit Windows 7 DVD you created and choose your version, Custom install using Advanced drive tools to delete existing partitions, create New as you wish, and format before install. Choose to remain connected to internet during install and plug ethernet.
After install, activate from the key on the Upgrade DVD you received (may require a robo call to MS), get latest drivers from WIndows Updates, and other missing drivers/apps from the Support>Downloads page for your model. Adobe Reader/Flash and Java runtime/free Ofc. are at their websites.
Your mileage may vary.