Why there's multiple instance of root and www-data user?

When I am using top command and pressing shift m, I get this

 7691 www-data  18   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7693 www-data  17   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7694 www-data  16   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7695 www-data  18   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7696 www-data  21   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7698 www-data  15   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 8027 www-data  18   0 82108 4200 1020 S    0  1.1   0:00.00 apache2
 7697 www-data  18   0 82056 4192 1020 S    0  1.1   0:00.00 apache2
11830 root      18   0 82108 3656  500 S    0  1.0   0:00.00 apache2
11831 root      18   0 82108 3656  500 S    0  1.0   0:00.00 apache2
25149 root      15   0 82108 3656  500 S    0  1.0   0:00.00 apache2
25151 root      15   0 82108 3656  500 S    0  1.0   0:00.00 apache2
14315 root      18   0 82108 3656  500 S    0  1.0   0:00.00 apache2
14644 root      15   0 82108 3656  500 S    0  1.0   0:00.00 apache2
 6959 root      18   0 82108 3656  500 S    0  1.0   0:00.00 apache2

Why there's two users exist for apache? and is it giving impact to free memory? root has a lot of apache instance & www-data too.

While I want to decreasing the MaxServer configuration into 5 on apache.conf and I get suprise while seeing the top report.

I am using mpm-itk for the apache.

Could you please enlight me. Thank you.