You can export content out of one blog and import it into the other blog. See here:
Log into ONE blog ie. the one you want to move content out of > go to Tools → Export, and download the XML (WXR) file to your computer.
In the the other blog ie. the one you want to move the content into > go to Tools → Import → WordPress, and upload the file you downloaded in step 1. After you upload the file, you can choose the option to Download & import file attachments if you want to move your media files.