I agree with Andy, very nice work indeed Alberto !
If you don't have a photo-editing system, then download 'Irfanview'. It's free, and very easy to use. Basically, you select 'Re-size/re-sample', and then type in (in the boxes shown on screen) the size you require. for the forum, the maximum is 800 x 600 pixels. This can then be saved, or, if you want to retain the original image in its original size and format, you can 'Save as', which allows you to save the altered image separately.
The programme also allows you to crop, adjust colours, sharpen and so on, and it also provides another form of filing system for all your images.
Wojtek directed me to it a few years back, and it's one of the best things I've used, even though I have 'Photoshop'.
Once you've downloaded it, if you have any questions, just shout!