Acer normally provides a Drivers
&Apps CD with their Upgrade kits? Do you have this? If so then you have on there the programs that are preinstalled on 32 bit Acer which you cannot carry over with a 64 bit install.
Make your Recovery Disks first so you have a path back to factory condition, then back up your files and boot the 64 bit DVD, select Custom install, Delete all partitions, create New partition(s) as you wish, format before install. Clean Install Windows 7
The installer is mostly driver
-complete, with newer drivers arriving quickly in Optional Windows Updates. If any drivers are then missing in Device Manager, suggest you find the latest ones on the Acer Support Downloads webpage for your model. Make sure your wireless driver is on CD or load it to flashstick beforehand in case you need it to get online.
After you have it setup as you wish, make a Windows 7 backup image so you never have to reinstall, just reimage the HD or a replacement in 20 minutes.
If you only want to try and compare 64 bit, you can shrink the existing Windows 7 in Disk Management to install it to the new space. Windows will configure a dual boot menu to choose which one you want to boot. Partition or Volume - Shrink