Upanayana is an important Samskara, duty of a Hindu.
The three Varnas, Brahmana, Kshatriya and Vaisya must have this performed.
Read my posts on Samskaras.
The wearing of the sacred thread opens the inner eye.
One becomes a Dwija, born for the second time.
The Upaveeda must remain clean.
It has to be changed periodically.
It is also changed for special occasions like Marriages,Homas,Poojas,Apara Kriyas.
Following is the mantra for changing the Upaveeda.
The removed Upaveeda msu no be deposited in a Garbage bag or thrown out.
It may be deposited ,if you have a Garden,in a small pit.
Otherwise drop it in a pit, close it in any clan place.
a.Aachamanam:Shuklaam Bharadharam………. Santhaye
c.Mamo patha samastha duritha kshya dwara sri paameshwara preethyartham
Sroutha smartha vihitha sadachara nithya karmaanushtanaa yogyatha sidhyartham brhma teja abhivrudyartham yagnopaveetha dharanam karishye.
d.Yagnopaveetha dharana maha manthrasya
Parabrhma rishi(Touch forehead)
Trushtup chanda (touch below nose)
Paramathma devatha (touch heart)
e.Yagnopaveetha dharane viniyoga
Wear Poonal one by one by reciting(poonal should be held by both hands, the tie in the poonal being held above by the right hand facing upwards)
Yagnopaveetham paramam pavithram praja pathe,
Yat sahajam purasthad aayushyam
Agriyam prathi muncha shubram yagnopaveetham balamasthu theja.
f.After wearing all poonals one by one do Aachamanam
g.Remove the old poonals and break them to pieces by reciting
Upaveetham bhinna thanthum jeernam kasmala dooshitham, visrujami na hi brahma-varcho deerghayurastu me
Summary meaning: I wear the white yagnopavitha that is purifying , which was born along with brahma, which is capable of increasing life .I am sure this would give glory and strength to me.I am destroying the dirty , soiled yasgnopavita .
Om That Sat,