How do I increase the voltage limit by connecting same capacitors?
ON DC

If you have two 100V rated capacitors in series, you cannot assume that the combination of the two will be 200V. Slightly different leakage currents will mean one cap has more voltage across it than the other. 

This can be mitigated by adding resistors across each capacitor that have values lower than the effective leakage resistance of the capacitors. If the cap has a leakage R of (say) 10M\$\Omega\$, go for 1M\$\Omega\$ resistors. Any variation will be reduced by about 10:1 BUT, I'd suggest you wouldn't get better than 1.9 x original voltage rating.

ON AC

This is determined by the capacitor values so if one capacitor is smaller than the other, it will receive more AC volts across it.