Why does itunes fails to update even though previous version is installed successfuly?

Trying to install iTunes 14.7.4 latest version. I had problems trying to install the previous version and spent many hours deleting everything Apple from my Windows 10 32 bit machine. The machine is well within the required specification for iTunes. I finally did fix it, and then, another update two weeks later!

I get errors initially saying that the update failed and that I should use Tools > Download Only, and then Ii have tried installing the iTunes installer file with the Appdata > Local. I then get the error that another install is in progress (probably the initial attempt as no other installs are taking place on my computer). I did restart my computer anyway and immediately tried the manual install as above. But I get the same error.

I could use my Revo Pro software to uninstall and do some registry tweaking myself, and once again delete all Apple folders and files, but this should not be necessary at every update! I have the iTunes helper enabled now, so I may try restarting and installing again.

I have tried switching off my Antivirus to no avail. I have no viruses etc, on my machine. I will try a Microsoft tool again to help look at any install problems, but last time weeks ago this did not help.

Simply uninstalling the iTunes program in Windows and reinstalling produces the same error. So it is a complete deletion or other option.

Any help is appreciated!

James.