Welcome to SW forums Thomas
Student version software is different than commercial version. A student version is generally one version below the commercial version. If you try to use data from student version to commercial version, you will get a watermark in the drawings and other way you can't open a commercial version file into student version until unless you have higher student version.
So depending on what type of version you have, the answer can be yes or no. But better to uninstall the current version (i.e. the one for 29 days) and install the student version. For more info on student version software, check here: http://www.solidworks.com/sw/education/mechanical-engineering-student-software.htm
Also read this post for your future reference: Forum Posting
Thank you for your quick reply. I was hoping that all I had to do was to uninstall the old student version and replace with new and the 12 month licence.
My best regards,