Upgrade in-place with low disk space on C: drive I am due to upgrade SQL Server 2005 Express to 2014 Express. This will be an in-place upgrade.

It's not my preferred way of upgrading, but being a physical machine and in a specific secure network zone, it has to stay put &amp; keep its instance name, so it must be an in-place upgrade.

The only small issue is there is just under 10% free space available on the C: drive (the drive has 3GB space left). I hope to upgrade in-place and then once complete, go through getting disks replaced for bigger disks etc. (this is due to project upgrade deadlines).

Could someone tell me how much extra space will be put onto the C: drive with a SQL Server Express 2014 upgrade, please? Note no system databases live on the C: drive. Sadly no housekeeping can be performed by the Windows team etc.
Can you do it? Yes, you can. Should you do it? No, no shouldn't.

You're playing with fire, less than 10% free space on C drive is an urgent/critical flag in any decent company.

If you spot anything worth deleting, go for it. But in any case, since this is a physical server and you said Wintel team can't help you, present the scenario as an issue and a possible emergency in the future.