Specify a ratio using [] and [].
Press [Reduce / Enlarge].
Select a preset ratio which is close to the desired ratio.
Adjust the ratio with [] and [].
Pressing [] or [] changes the ratio in increments of 1%. Pressing and holding down [] or [] changes it in increments of 10%.
Press [OK].
Place the originals, and then press the [Start] key.
To change the value you specified, readjust it with [] and [].