To change the default font size of a LaTeX symbol or a text add the below package in your document

\usepackage{lmodern}

Use the below command to change the font size of a symbol or a text and also its type

\fontsize{size}{baselineskip}\selectfont

The command font size has three arguments

First is size

The second is baseline skip and

The third is to select a font

#### Change the font size of a symbol or a text

{\fontsize{10}{10.5}{ $\alpha$}}

{\fontsize{00}{10.5}{$\alpha$}}

{\fontsize{30}{10.5}{$\alpha$}}

{\fontsize{40}{10.5}{ $\alpha$}}

{\fontsize{50}{10.5}{$\alpha$}}

{\fontsize{60}{10.5}{$\alpha$}}

{\fontsize{70}{10.5}{$\alpha$}}

{\fontsize{80}{10.5}{$\alpha$}}

{\fontsize{10}{10.5}{$\alpha$}}

{\fontsize{100}{10.5}{ $\alpha$}}

#### Predefined command to change the size

Here are some predefined commands that you can use without adding any package

Tiny
{\tiny Tiny}
Script
{\scriptsize Script}
Foot
{\footnotesize Foot}
Small
{\small Small}
Normal
{\normalsize Normal}
large
{\large large}
Large
{\Large Large}
huge
{\huge huge}
Huge
{\Huge Huge}

#### Change the font type of a text and its size

{\fontsize{50}{10.5} ${\rm Roman}$}

{\fontsize{50}{10.5} ${\em Enfático}$}

Below are some more font types that you can use

{\rm Roman }

{\em Enfático}

{\bf Negrita }

{\it Itálica }

{\sl Slanted }

{\sf Sans Serif }

{\sc Small Caps }

{\tt Typewriter }