Hey, you're lucky! When the V1 was popular, all my friends who had Tama's were terrible caretakers and were constantly leaving me to Tama-sit so they could have Mametchi's. So, you want a change? Let me intervene. Here's some tips on getting other characters.
Tarakotchi: Feed it meals as the hearts empty, but remember to constantly let the happy hearts drop. When it beeps because of lack of happy hearts, don't play with it. Feed it snacks. With discipline, only give Time Out's, NEVER praise. Poor guy...but that will get you a Tarakotchi.
Hanatchi/Androtchi: Basically, do the opposite as you would for Tarakotchi. Feed it snacks to keep it happy, but let it beep at you for meals. Once, and only once, may you ignore the beep for food and make it sick. Try to let it sleep with poop next to it. Also, only praise, NEVER give it Time Out's.
I can't remember how to get Kuchipatchi/Memetchi, but as soon as I remember, feel free to ask me how to get them.