Please advise to increase the oracle data buffer quality from 96% to 99.7%

Dears,

1.Current system oracle data buffer quality is 96%, if want to increase to 99.7%,

some db parameters as below, how to tuning the related parameters ?

SGA = 48G

PGA = 12 G

Db_cache = 19840M

Shared_pool_size=4G

2, ST02 shows some red colour's swap for some buffer, how to avoid it to happened ?

which parameter need to tuning ?

Thanks,

Michael