Since semen is considered to be very precious, how to preserve it make it raise to head (ojas)?
The state where the semen's natural downward flow is blocked and it is made to travel up as Ojas is known as Urdhareta.
This is difficult to achieve but can be achieved through the practice of Yoga.
As, you may know, Yoga is eight-limbed:
yamaniyamasanapranayamapratyaharadharanadhy anasamadhayo-a-shtava anggani|
Yama, Niyama, Asana, Pranayama, Pratya hara, Dharana, Dhyana, Samadhi, are the limbs of Yoga.
And, under Yama, comes the following:
ahinsasatyasteyabrahmacharyaparigraha yamah |
Non-killing, truthfulness, non-stealing, continence, and non-receiving, are called Yama.
Now, the result of Brahmacharya is stated to be Viryalabha or getting the state of Urdhreta.
- बहचमपय णतषामां वीमरय ाब् ॥ ३८॥
By the establishment of continence energy is gained.
All these verses are from Patanjali Yoga Sutras' Chapter 2 (Sadhana Pada).
So, basically the answer is that by following continence/Brahmacharya one can achieve the state where the sexual energy is not wasted but instead is converted into spiritual energy (Ojas).
And, Brahmachrya basically means to give up all forms of sexual conducts although it has a different definition for married persons.
While it's very easy to say that, by maintaining Brahmachrya one can raise the sexual energy upwards, but that is difficult to achieve that practically and hence not much helpful as an advice.
So, let me also add to this answer few Yogic postures (Asanas) that help one to curb one's sexual desire and thus aids in Brahmacharya.
I have this book called " Yoga Sadhana and Yoga Chikitsa Rahasya by Swami Ramdev". From that book I have selected three Asanas/Mudras.
- Aswini Mudra:
This is discussed in this post.
This Mudra is said to curb sexual desire and helps in attaining Urdhreta.
- 2.Brahmacharya Asana:
This is said to be extremely helpful in Brahmacharya (as the name itself suggests) and it also cures diseases like Swapnadosha (nightfall). Not that difficult to master this posture too IMO.
- Go Raksha Asana:
The benefits of this Asana are the same as those of the previous Asana. But this is somewhat difficult to master compared to the other one (at least for me).