Synthetic steps for the interconversion between aldehydes and ketones
You can easily convert aldehydes to ketones and vice-versa by using simple organic synthetic steps which are very much well known.

Converting aldehydes to ketones

For converting aldehydes to ketones there are numerous pathways. Here I am mentioning the simplest two ways, one of which is by using Grignard reagent and other by using thioacetal intermediates. 

You can react aldehydes with Grignard reagents ($\ce{R^2 -MgBr}$) and perform acidic workup to generate secondary alcohols. Then you can oxidise the alcohol to get a ketone by commonly used oxidising agents like PCC (pyridinium chlorochromate). 

The other way is to react the aldehyde with a propane-1,3-dithiol to generate a cyclic thioacetal . Now, interestingly, the proton attached to the carbon now can be removed by strong base like n-Butyllithium, and generate  Carbanion which can perform a $S_N2 $ reaction with an alkyl halide to generate cyclic thioketal. After that the thioketal can be hydrolysed using $\ce{HgCl2/CdCO3/H2O}$  to generate your desired ketone. 



Converting ketones to aldehydes

The easiest step for this conversion is to perform a Bayer-Villiger Oxidation reaction on the ketone to get an ester. Then that ester can be reduced by Diisobutylaluminium Hydride (DIBAL-H) and an aqueous workup will generate desired aldehyde (along with an alcohol). (If you wish you can further oxidise that alcohol also in case you want aldehyde of that part).