Can DC voltage be stepped up by some means as AC can be stepped up by using transformer?

There are a few ways to step up DC.

The first is to chop it (square wave) and run it through a transformer. Rectify it, and it is DC again.

There is another way, by using a boost converter. This method does not use a transformer, but does make use of an inductor to store charge for a short period of time. An oscillator will short the inductor to ground, and when it is turned off, the inductor will release its charge as a higher voltage. Here is a primer on the concept:

http://services.eng.uts.edu.au/~venkat/pe_html/ch0...

First you have to turn it into AC and then you can use a transformer to change it to another AC voltage, after which you can rectify it back to DC.

This is how a DC-DC power supply works.

The method most commonly used in a DC-DC converter is indeed to convert it to AC and transform it. You could use the DC input to charge each capacitor in a series string, one at a time. But the complexity and instability of such a circuit makes it impractical.

An older method once common was a motor-generator.

There are DC multiplier circuits that can boost DC output voltage through an arrangement of series capacitors and diodes. However, the trade off for higher output voltage is a reduction in output current handling capacity. So, what you get is higher output DC voltage at a lower operating current.

An example of this can be found at: DC Voltage Multiplier Circuit Plans

http://www.reuk.co.uk/DC-Voltage-Multiplier-Circui...

This, however, may not be exactly what you had in mind.

See: Voltage multiplier

http://en.wikipedia.org/wiki/Voltage_multiplier

May be more what you're looking for.

DC voltage can't be stepped up

it is possible by other means. convert dc into ac, use trasnsformer to step up and then conver it into dc by using rectifier