Hello dear aspirant.

You are talking a very good call. For this you can reach your regional NIOS office they will guide you through the process.

Yes you can surely take maths and leave biology.

Actually there in NIOS a option of TOC (transfer of credit) is available in which you can get marks of your three subjects from previous year record and hence you have to give only two papers and get a result.

Hope it will help you.

You should go to NIOS office for this.

All the best.