After taking bath, sit on a clean mat/rug and do aachaman. Take the new Yagnopavit and chant these mantras "Aapo Hishtha!" and perform abhishekam with water on Yagnopavit.Chanta these mantra before wearing the Yagnopavit.
" Om Yagnopavitam Param Pavitram Prajpateryatsahajam Purastaat|
Ayushya Magrayam Pratimushcharu Shubhram Yagnopavitam Balamastu Tejah||
After chanting this mantra, wear the new Yagnopavit and atleast 20 times chant the "Gayatri Mantra". Take out the old Yagnopavit and chant this mantra "Samudram Gaccha Swaha" and put it in the water (Sea, River, Lake or plants).
