Setting Up My AI Files To Print IN Various Sizes

Design details: I would like someone to show and do how to set up some AI files is have so they can be printed by others in different sizes without losing the quality.

I want them to be able to produce high quality finish in different sizes. My files are set up like cards at present so they may need to be increased in size. And change the paper size.
Target audience: kids / parents
Ideas for the visual style: n/a
Things to avoid: n/a
Preferred colors: n/a
Where the design will be used: print
Extra notes: I would like someone to show and do how to set up some AI files is have so they can be printed by others in different sizes without losing the quality.

I want them to be able to produce high quality finish in different sizes. My files are set up like cards at present so they may need to be increased in size. And change the paper size.

5 high quality JPG files (res. : 300 dpi) in various sizes:
e.g 5 high quality JPG files (res. : 300 dpi) in various sizes:

★ 2x3 ratio - for printing -
Inch: 6x9, 8x12, 10x15, 12x18, 16x24, 20x30
Cm: 15x23, 20x30, 25x38, 30x45, 40x60, 50x75.

I presume will need to set it so when I save as pdf they can print in any size. Please only apply if you know how to do this. I would like one to be done today, so I can take to the printers and test our.

For each one I will pay £2.00

I have a few to do , so will put the price at
£10 so I can get five done.

THKS