A few questions to narrow down the problem:
* Are there any additional error or warning messages?
* Can you make sure the directories are writeable and correct ownership?
* Could you try the option to install from a directory instead of uploading the package file?
Ahh, having the exact error message helps. Can you check out our
Common Support Questions
for "The installation package fails to upload". It's usually the upload size is smaller than the installation package. Try that and let me know if you're still having problems.