Kathrine,
Within the settings section of each module, you can hide the title and all of the other controls such as +/-, print, and syndicate by hiding the module container. Under module settings, remove the check by "Display Container". This also hides the container colors and borders though. If showing the container, you can hide controls such as the +/- by setting "Visibility" to None, and separately remove the check by Allow Print, and Allow Syndicate. All within Module settings.
To show the container, but remove the title, that would require a customized container.
If you have not made your own skins before, you can start with making a copy of the standard DNN skin and container files, and see how they are built, or edit them to make your own version. You can find them under the folders Portals/_default/Container or Portals/_default/Skin Folders, but be sure to copy them instead of editing them there, since these could change with DNN upgrades.
As an example, copy the contents of one of the container folders, which includes a .css, .xml, images, and htm files. There will be an .htm file for each container type such as "text header -/ white background.htm" Edit the .htm file carefully, such as to remove the title and possibly the line below it. Then, rename this file to something unique. Edit the .css file to change color settings if you like. Then zip the .css, .xml, images, and the newly edited .htm file together. Name the .zip file to something unique, which will become your new container name, such as MyContainer.zip, and upload it into your portal through the Skins option, under Admin or Host (there will be a link to upload container).
To apply the new container to a module, open module settings, and look for the "Module Container" field, and select your container from the list. If you uploaded it as Admin, it would be a "Site" container, if you uploaded with Host, it will show under the host containers.