Here's how I interpreted the OP's situation. Currently in HS, has the NROTC scholarship in hand, currently placed at USC (applied under Chem Eng major), accepted into UCLA as well (applied under Chem major), and is looking to switch his scholarship placement and major.
If my understanding is correct, then Ew3081, this is not complicated.
You should call UCLA NROTC unit, advise them that you are thinking about moving your scholarship from USC to UCLA, with the intent to study Chemistry, a Tier 2 major. The PNS at the NROTC unit (in this case UCLA) is the approval authority to move from Tier 1 to Tier 2. Ask them to confirm if this is something the CO would support/approve. Contrary to another post here, there is no tier change board for moving from Tier 1 to Tier 2, only a board for moving to Tier 3 or LREC.
If the UCLA NROTC unit is supportive (and I expect they would be), you will then send an email or call the number below and request your scholarship to be moved to UCLA:
After You Are Selected
If you have been awarded an Navy ROTC scholarship and have questions about placement or if you have a school change request:
1.800.NAV.ROTC Option 3, Ext. 8,9
Contact the Navy ROTC Unit Placement Office: pnsc_nrotc.placement@navy.mil
BUT, as Pima correctly points out, graduate school opportunities out of NROTC are rare and should not drive this decision.