How can i adjust the voice clarity and volume in my Nokia 3210 classic mobile phone?

I am having a real problem hearing the callers voice on my phone and I have tried to adjust the clarity but am noticing no difference. Any suggestions?How can i adjust the voice clarity and volume in my Nokia 3210 classic mobile phone?While on a call, just try increasing the volume via the side buttons or try using the scroll keys. Like press the up or right scroll key. This might help.