Is it possible to adjust the angle more than I did: [ABOVE RIGHT]
\draw [black, thick] (0.7,0) arc [start angle=0, end angle=110, radius=0.7cm]
node [above right] {$\theta=\phi-\ang{90}$};
I'd like to remove it from the y axis and put it in more right than it is.
And How can I make a subtitle under this figure?
Voltage and current phasor of a capacitor.

\usepackage{tikz}
\usepackage{siunitx}
\begin{document}
\begin{center}
\begin{tikzpicture}[>=latex]
\draw[style=help lines] (0,0) (3,2);
\coordinate (vec1) at (110:2);
\coordinate (vec2) at (20:4);
\coordinate (vec3) at (0:4.5);
\coordinate (vec4) at (90:2.5);
\coordinate (vec5) at (270:1.5);
\coordinate (vec6) at (180:3);
\draw[->,thick,black] (0,0) -- (vec1) node[below left] {$\hat{I}$};
\draw[->,thick,black] (0,0) -- (vec2) node[below right] {$\hat{V}$};
\draw[->,thick,black] (0,0) -- (vec3) node [below] {$Re$};
\draw[->,thick,black] (0,0) -- (vec4) node [right] {$Im$};
\draw[->,thick,black] (0,0) -- (vec5);
\draw[->,thick,black] (0,0) -- (vec6);
\draw [black, thick] (1.3,0) arc [start angle=0, end angle=20, radius=1.3cm]
node [midway, right] {$\phi$};
\draw [black, thick] (0.7,0) arc [start angle=0, end angle=110, radius=0.7cm]
node [above right] {$\theta=\phi-\ang{90}$};
\end{tikzpicture}
\end{center}
\end{document}


\documentclass, the relevant packages and\begin{document}... \end{document}. Beyond that, could you please explain what you mean? Which angle? More right with respect to what? What have you adjusted it with respect to? I am not sure what you mean by 'subtitle'. Documents sometimes have subtitles. Do you just want a caption? If so, use\begin{figure}\centering\begin{tikzpicture}...\end{tikzpicture}\caption{My caption}\end{figure}, for example. – cfr Nov 05 '14 at 22:36