Image manipulationwith GIMP and convert

[Artur G. Sibagatullin]

Hello everybody!
In order to convert large amount of pictures I need a command-line
script which use convert command.
Thats why I got a question.
When I used GIMP, I did the following: reduce resolution of the picture
while number of pixel remain the same, at the expense of this the size
of the picture in inches get larger. After that by reducing the size in
inches I increased the resolution as high as it possible. As the result
I had smaller picture with quiet high resolution. How must I do that
using convert command?
Thanks!