He can achieve this in two ways: He can mend his emotive constitution, and he can strategize the way he thinks, speaks and acts.
Thought, speech and action are entirely under a person’s control! Changing one’s emotional instincts, in contrast, takes inordinate efforts that cannot be relied upon.
This is why G-d did not command Moses to spy on the Land of Israel. Moses sent spies on his own accord. But before Joshua took the Jews into the Holy Land, that's when G-d commands that he send spies, and then - only that they spy the city of Jericho - not the entire country. Jericho is the key to unlocking Israel!
Why only Jericho and not the entire country?
Spying out Jewish territory implies, at the spiritual level, inspecting one's own self for Torah-true resilience. The Jew's soul is his personal Holy Land. Spying out the entire Jewish land means spying out both one’s temperaments as well as one's behavior. In turn, conquering the Canaanite land means to overhaul the entire terrain, both emotive and behavioral. However, only the conquest of Jericho, one's behavioral component, can be relied on for full control.
This is why G-d commanded that only Jericho be spied out, be investigated to see if one’s own “Jericho” subserves G-d’s wishes. Jericho, which comes from the Hebrew word “odor”, relates to smell; Just as smell affects us, but leaves no imprint, so too thought, speech and action do not reside within us.
These 3 behaviors do not "own" the person. Speech and action certainly can be good or bad, completely under full control. Even a bad thought too, should it arise, can easily and effectively be deflected with a good one. In contrast, a poor emotional response cannot so easily be mastered.
These capabilities or energies derive from an outside - higher - source made available for our use; They are not as integrative with our being as are our emotive facets. We use them to interact, but they are not tightly bound into our constitution. These faculties are tools, as "ropes" to climb with, available at our behest. They provide us with choice under our full control. We can ascend with these ropes to draw ourselves higher. Other ropes, also of higher source, but of the negative kind, can also be used, only these would take the Jewish soul to a lower than original depth. The choice is either to climb up with them to noble loftiness, or use them to climb lower and deeper into a rut.
To analogize, think of a car. The car will not function unless gas “from the outside” is fed into it. Similarly, our souls access thought, speech and action from available external albeit higher divine sources.
Because of their higher point of derivation, these 3 faculties can raise the level of the soul to guarantee it attains a higher perch from the level it originated from in the first place. Why else was the soul sent down here into the nethermost of all worlds - if not to improve its lot?
(We spoke earlier of sources of divinity, how one is higher than the other - here.)
This is why how a person can better himself; By proper control of his "Jericho" - his thoughts, speech and actions. Like a circus acrobat who swings from rope to rope to reach a higher landing, so too the divine soul, by grabbing on to the right 3 "garments of the soul", can lift itself higher from where it initially stood.
Of course, the corollary of this configuration implies the person can also climb steeply downwards. For just as he can choose to deflect bad thoughts and change bad speech and behavior in favor of good ones, so too, by choosing the 3 garments purveyed by the Bovine Soul, his Divine Soul can be dragged to a level far lower from where it originated.