How to set icons to 32x32

There is no programmatic support yet. Currently it can be done by customizing itweak_upload.css file, or by overriding mime icons in theme CSS files.

Changing to "won't fix" for no activity for over 4 weeks. Please reopen it when you have a patch.

Heres the css to show attachment icons using the 32x32 set (modified from version 2.3, full css as attachment), would be nice if this could be choosen from the module without any css tweaking:

/* CSS Sprites */
table.itu-attachment-list .mime {
background: transparent url('images/mime-32.png') no-repeat center 0;
padding: 0 7px;
margin: 0;
width: 32px;
min-width: 32px;
height: 44px;
min-height: 44px;
}

/* Mime types */
.itu-attachment-list .mime-ai {
background-position: center -0px !important;
}

.itu-attachment-list .mime-odt,
.itu-attachment-list .mime-doc {
background-position: center -64px !important;
}

.itu-attachment-list .mime-eps {
background-position: center -128px !important;
}

.itu-attachment-list .mime-gif {
background-position: center -192px !important;
}

.itu-attachment-list .mime-gz {
background-position: center -256px !important;
}

.itu-attachment-list .mime-id {
background-position: center -320px !important;
}

.itu-attachment-list .mime-jpg,
.itu-attachment-list .mime-jpeg {
background-position: center -384px !important;
}

.itu-attachment-list .mime-pdf {
background-position: center -448px !important;
}

.itu-attachment-list .mime-png {
background-position: center -512px !important;
}

.itu-attachment-list .mime-pptx {
background-position: center -576px !important;
}

.itu-attachment-list .mime-ps {
background-position: center -640px !important;
}

.itu-attachment-list .mime-psd {
background-position: center -704px !important;
}

.itu-attachment-list .mime-mp4,
.itu-attachment-list .mime-avi,
.itu-attachment-list .mime-mov {
background-position: center -768px !important;
}

.itu-attachment-list .mime-rar {
background-position: center -832px !important;
}

.itu-attachment-list .mime-svg {
background-position: center -896px !important;
}

.itu-attachment-list .mime-swf {
background-position: center -960px !important;
}

.itu-attachment-list .mime-tar {
background-position: center -1024px !important;
}

.itu-attachment-list .mime-xls,
.itu-attachment-list .mime-xlsx {
background-position: center -1088px !important;
}

.itu-attachment-list .mime-zip {
background-position: center -1152px !important;
}

"Needs review" is applicable only to patches.

Another thought...
32x32 icons should be an option, configurable in module's settings. Otherwise users of this module should edit .CSS file in their theme. Based on the state of solution in this issue it can be closed as support request. as feature request it needs work. Please reopen if you have a patch with configuration in module's settings.