Enlargement of the testicles themselves is nigh impossible without surgical implants or long term pumping (both of which I wouldn’t really recommend unless you’re DESPERATE for bigger balls)
There is one thing you can do - manually, that will increase their size in appearance only though, you will not get any additional flesh. And that is manual stretching.
try stretching just the sac skin by itself lightly, pulling it out as far as is comfortable each time, just take it easy.. after you get the hang on skin stretching, add in ball stretching too, but be ESPECIALLY CAREFUL when you do that! the cords are fragile little things you know, and you can fuck yourself up bad by pulling too hard too soon. It’ll take a few weeks, but your balls will hang and flop around instead of being tight and ‘small’ looking.. they will LOOK bigger but will not actually BE bigger (the testicles I’m talking about, they will jiggle around in your enlarged bag)
If you want to increase the size of the actual balls inside the sac probably the easiest method is pumping. also this should be taken really slow and easy especially at first. I have seen pics of guys who have pumped up their balls over a few hours and gotten tennis ball size things or bigger but the effects only last a day at max, and then it’s back to pumping again. Of course they say if you do it every day eventually they stay big, but thats also what they say for penis pmping and there isn’t much evidence for it being true.
I myself have personally not gone more than about 30 minuites to get to about golf ball size, it is quite fun, there is no pain or weird effects if you do it right either, but the effects do wear off after a couple of hours although the sac will hang nice and heavy for a day or so after.
Beware that the long term effects of pumping balls (as well as the penis) are not known. For all you know you could be slowly making yourself sterile. Of course this alarmist stuff could all be bullcrack, but you can never be too careful with your little soldiers…
I’ve also heard of massages etc to enlarge the balls but I doubt whether this would be very effective.
I think that was worth more than 2 cents :)