This is an irregular verb. It follows the conjugation pattern of the verb volar.
Stem Change: o ue (suelto)
PresentPresente
El niño suelta la mano de su madre.
The boy lets go of his mother's hand.
PreteritePretérito indefinido
Soltaron al pájaro en el bosque.
They released the bird in the forest.
Negative ImperativeImperativo negativo
No sueltes la cuerda.
Don't let go of the rope.