If it is hard coded to go onto C: (or the System Partition) then you are limited in what you can do, but most software offers
you preferences early on in the Setup to select a location to install the program to a specific location, such as another folder
or drive of your choice.
Make sure you run the Setup as an Administrator so that access permissions don't become a problem, and read the
messages and options displayed by the Setup carefully.
4GB is too small for Windows to breathe and spread its' wings. You can try cleaning up your C: drive but anything like that
will be a very temporary solution at best.
Hard Disk still full after deleting large files
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Relocating Hard Drive Capacity and File Compression
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A better option would be to look at third party solutions that can Resize Partitions, hopefully without losing important data,
99.9% of the time these work perfectly, but there is a risk, so you must back up your valuable data somewhere safe and
away from the computer.
"Resize partitions - Can both shrink and expand FAT/FAT32 and NTFS partitions. Can also easily resize extended partitions
from either end."
BootIt NG
New, Free, Graphical Partitioning Tool
How to resize NTFS Partition?
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Of course you can re-install Windows elsewhere on your larger Partition. You can buy an extra bigger hard drive and install it on there.