  Let $X$ be a K3 surface, let $C$ be a smooth curve of genus $g$ on $X$, and
let $A$ be a line bundle of degree $d$ on $C$. Then a line bundle $M$ on $X$
with $M\otimes\mathcal{O}_C=A$ is called a lift of $A$ . In this paper, we
prove that if the dimension of the linear system $|A|$ is $r\geq2$,
$g>2d-4+r(r-1)$, $d\geq 2r+4$, and $A$ computes the Clifford index of $C$, then
there exists a base point free lift $M$ of $A$ such that the general member of
$|M|$ is a smooth curve of genus $r$. In particular, if $|A|$ is a base point
free net which defines a double covering $\pi:C\longrightarrow C_0$ of a smooth
curve $C_0\subset\mathbb{P}^2$ of degree $k\geq 4$ branched at distinct $6k$
points on $C_0$, then, by using the aforementioned result, we can also show
that there exists a 2:1 morphism $\tilde{\pi}:X\longrightarrow \mathbb{P}^2$
such that $\tilde{\pi}|_C=\pi$.
