In TikZ (and circuitikz
is based on TikZ) you can move anything by saying
\begin{scope}[xshift=<some x shift>,xshift=<some x shift>]
<contents>
\end{scope}
or
\begin{scope}[shift={(<delta x>,<delta y>)}]
<contents>
\end{scope}
so
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[american]{circuitikz}
\usetikzlibrary{arrows}
\begin{document}
\begin{circuitikz}
%Primer circuito
\draw (-6,-1.5)
to [V, v=$V_i$,invert] (-6,3)
to [short] (-3,3)
to [diode] (-3,1)
(-3,3) to [short] (0,3)
to [battery, label = 1V] (0,1)
(-3,1) to [R=$1k\Omega $,v = $V_o$] (0,1)
(0,1) to [R=$2k\Omega$] (0,-1.5)
(-3,1) to [R=$2k\Omega$] (-3,-1.5)
(-6,-1.5) to [short] (-3,-1.5)
(-3,-1.5) to [short] (0,-1.5)
(-3,-1.5) -- (-3,-1.7) node[ground]{}
;
\begin{scope}[xshift=-10cm,yshift=-6cm]
%Segundo circuito
\draw (4,-1.5)
to [V, v=$V_i$,invert] (4,3)
to [short] (7,3)
to [diode] (7,1)
(7,3) to [short] (10,3)
to [R=$1k\Omega$] (10,1)
(7,1) to [diode] (10,1)
(10,1) to [R=$2k\Omega$, v] (10,-1.5)
(7,1) to [R=$2k\Omega$] (7,-1.5)
(4,-1.5) to [short] (7,-1.5)
(7,-1.5) to [short] (10,-1.5)
(7,-1.5) -- (7,-1.7) node[ground]{}
;
\end{scope}
\end{circuitikz}
\end{document}

Please note that you could avoid much of this by changing your approach. I am not going to discuss all possible improvements. Rather, I will focus on the TikZ-specific ones and units. I also won't change the arrows
library since you seem to be happy with what it gives you. However, I'd lie to advertise
- relative positioning, and
siunitx
.
With these the code becomes
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[american]{circuitikz}
\usepackage{siunitx}
\usetikzlibrary{arrows}
\begin{document}
\begin{circuitikz}
%Primer circuito
\draw (-6,-1.5)
to [V, v=$V_i$,invert] ++ (0,4.5)
to [short] ++ (3,0)
to [diode] ++ (0,-2)
++ (0,2) to [short] ++(3,0)
to [battery, label =\SI{1}{\volt}] ++(0,-2)
++(-3,0) to [R=\SI{1}{\kilo\ohm},v = $V_o$] ++(3,0)
to [R=\SI{2}{\kilo\ohm}] ++(0,-2.5)
++(-3,2.5) to [R=\SI{2}{\kilo\ohm}] ++(0,-2.5)
++(-3,0) to [short] ++(3,0) to [short] ++(3,0)
++(-3,0) -- ++(0,-0.2) node[ground]{};
\draw (-6,-8.5)
to [V, v=$V_i$,invert] ++(0,4.5)
to [short] ++(3,0)
to [diode] ++(0,-2)
++(0,2) to [short] ++(3,0)
to [R=\SI{1}{\kilo\ohm}] ++(0,-2)
++(-3,0) to [diode] ++(3,0)
to [R=\SI{2}{\kilo\ohm}, v] ++(0,-2.5)
++(-3,2.5) to [R=\SI{2}{\kilo\ohm}] ++(0,-2.5)
++(-3,0) to [short] ++(3,0)
to [short] ++(3,0)
++(-3,0) -- ++(0,-0.2) node[ground]{};
\end{circuitikz}
\end{document}
As you see moving the circuit it even simpler since all coordinates are relative to the first one. I find them more intuitive, too. And with siunitx
you achieve consistent typesetting of the units.