You can increase the amount of DNA but be careful if the template is overload smearing may appear in the gel. We usually use in the range of 10-100 ng DNA per reaction. If possible try to optimize the condition like annealing temperature.

Thanks for your reply Chongtham Rajiv...

It is also necessary to use this interval for real time PCR ? (10-100 ng DNA)

I'm based on a range of 30-100ng 

You can choose an optimum conc. from this range. For my case, I used 10 or 20 ng of template per reaction for realtime pcr and it gives good result.

Good luck.