Thumbnail's Size

Change the dimensions in Settings -> Media then run the Regenerate Thumbnails plugin.

but the thumbnail’s size is not matching with the one in Settings -> Media, which means thats not the size from where the thumbnail is being generated..

In that case, it must be a custom post thumbnail that is being generated in your theme using add_image_size(). Try looking in functions.php.

the thumbnail’s link is this:

https://graviteti.com/arena/wp-content/themes/eCommerce_v1.8.2/thumb.php?src=https://graviteti.com/arena/wp-content/themes/eCommerce_v1.8.2/images/dummy/s5.jpg&w=210&zc=1&q=80&bid=1

you can see the code at the end, which is forcing the image to resize, i’m talking about the peace in bold:
What should I change in that peace, so the image becomes for example 150×150

(I’ve fund where to change that value in the code)

As this is a commercial theme, we cannot really help. You need to seek support from the theme vendors: https://templatic.com/support

I don’t think that the problem should be somewhere else ??
it has to be simple.. ??

Just FYI, that Theme is using TimThumb to generate Thumbnails.

But as for Theme-specific support, please refer to the link @esmi provided.

The theme is using this file: thumb.php to resize the picture’s thumbnail and show it in the front page.

here is an example of how all of that is done:

graviteti.com/arena/wp-content/themes/eCommerce_v1.8.2/thumb.php?src=https://graviteti.com/arena/wp-content/themes/eCommerce_v1.8.2/images/dummy/a7.jpg&w=210&zc=1&q=80&bid=1

bold – the thumb.php file is being called,
italic – to resize the X picture
bold – with these parameters.

– I tried to find where the last part of the link (in bold) is being given, and I found it here:

https://img194.imageshack.us/img194/1185/screenshot001qr.jpg

As you can see I’ve already changed the values in that peace of code, but no effect is being shown in: https://www.graviteti.com/arena :/

This is a commercial theme. We cannot help. Try posting on https://templatic.com/support