[Plugin: WP FLogin] Custome Logo

you should editate the file template_mid_footer.php in the plugin “File editor”, inserting a line like this:

<div align="center"><img id="mylogoabove" src="/tstgsn/images/logo_alpha.gif" alt="logo_above" /></div>

the mid_header.php solved the problem, thank you.

one last thing, how can I minimize the distance between the image and the top of the login box?

It depends by the Theme: you should work with css, try e.g. setting
#login {
margin-top: 0;
}