ACM document format vertical space

It is my first time writing a document using the ACM class (sig-alternate). However, I am encountering a big vertical space on the first column of my first page, that shifted 5-6 lines of my Introduction to the second colum (see picture below). I have tried to use the command raggedbottom but it doesn’t change anything. I suppose this is due to the ACM acmcopyright command, which, if setted correctly, add a small copyright text which almost fill the gap you can see on the figure.
Finally, I don’t understand how to get rid of the ISBN and DOI for now. On the proceedings I have read which used the same class, no DOI or ISBN appeared. Thanks a lot for your help.