The transformation you are referring to, where a down quark changes into an up quark, is known as a quark flavor transition. Specifically, it is an example of a weak decay process involving the weak nuclear force.
In the Standard Model of particle physics, the weak force is responsible for interactions that involve changes in the flavor of quarks. During a quark flavor transition like the one you described, certain conservation laws must be upheld. One such conservation law is the conservation of electric charge.
The down quark has a charge of -1/3, while the up quark has a charge of +2/3. When a down quark changes into an up quark, there is an increase in electric charge by +1. To conserve electric charge, another particle must be produced or absorbed to balance the change.
In this case, the weak decay process involves the emission of a W- boson, which carries an electric charge of -1. The W- boson then decays into an electron (e-) and an electron antineutrino (νē). The electron carries a charge of -1, while the electron antineutrino has no electric charge.
So, when a down quark turns into an up quark, an electron and an electron antineutrino are released to conserve electric charge. This process is an example of the weak force-mediated decay and is one of the ways in which flavor-changing processes can occur in particle physics.