First, which version of Visual Studio are you using? It should not matter which folder you installed it into.

Second, to run powershell scripts, you need to specify the full path to the file, so your file should execute if you use the following:

c:\scripts\ps\changeimagetype.ps1

to get that on the command line quickly, you can type .\ch then press tab - which should resolve the filename.

the other thing which may stop you is the executionpolicy,

Type

get-executionpolicy

to find out what it is. It's likely set to "All Signed" which means your script would have to be signed.

You can find out how to sign scripts by typing

get-help about_signing

Alternatively, you can change the executionpolicy using

set-executionpolicy "unrestricted"

which will allow all scripts to be executed.

Hope this helps, for more info see the Powershell episodes on the DFO Show.