But what exactly do you want help for? Is the problem that your wife feels the size of your genitals aren't large enough, or is there some other problem (e.g. fertility) where she is assuming the size of testicles makes a difference?
In terms of your appearance there really isn't much you can do unless you want to speak to your doctor about the possibility of scotal/testicular enlargement. This is basically a form of cosmetic surgery and something you can easily find out about by using a standard search engine.
If the problem relates to something else, for example erectile dysfunction or fertility, then that is a different issue.