I presume that to use GParted to sort out the Linux partition I have to go into Ubuntu and download and install it there
No need - it's included in Ubuntu - and in most distros, including Puppy.
It can't resize partitions which are actually being used - if you have a look at the screenshot (told Steve he was going to regret teaching me that, but I'm still very grateful) in post 806, you'll see that two of the partitions have a symbolic key next to them.
That means that they are locked away from GParted's activities beyond a simple scan - and they are the partitions in use by the distro I was running at the time (Mint). Prevents a distro wiping itself off the hard drive.
It could, however, modify any of the partitions not currently in use.
The best way to run GParted is from a live CD, which allows you to do whatever you wish to any partition on the computer. This makes it useful to keep a note of the details of your various partitions, including their size, to double-check that you're deleting the correct partition.
In reality, the risk is very small. The experts always seem to recommend backing up data before any partitioning, just in case.
If it's any help, I've installed all sorts of stuff that I never use - just for the fun of it, or to try something out. This has used slightly less than 4GB of the /root partition. I'd honestly be surprised if most of use ever needs a / partition larger than 5 or 6 GB. although I often see 10 GB suggested.
And usefully, modern Linux distros will read from and write to NTFS - so you can experiment with shared data partitions (allowing Linux and Windows some common storage space for files you want to use in both.) Perhaps ej could say more about this? I've only tried it a couple of times, and haven't used it as much as I anticipated.
One small caveat. If you download an infected file, it will almost certainly have no effect on your Linux installation. Opening it from the Windows installation could produce a surprise... On the remaining machine with a shared data partition, I scan files with Clam before saving them to the shared partition.
When I remember.