Hi Taolele,
If you'd like to purchase just the Semester 1 (6 months) Curriculum for LR and LM now and wish to upgrade to the Semester 1+2 (12 months) curriculum later on, you will simply need to sign in to your BrillKids Account and re-visit the Online Store. You will notice that you'll have upgrade options listed there, and this is how you can get your Curriculum upgrade.
You may find instructions in this Support article:
http://support.brillkids.com/index.php/article/upgrading-existing-product