I am trying to simulate a simple circuit using a simulation program like SPICE. In the beginning of the circuit I have a pulse train voltage source, later it is connected to a normal LPF. The voltage source frequency is set as 1 kHz, my question is how to increase this frequency? 

The only options that I have is to change the time of the cycle and the voltage. If I set 1 ms and 5V, the frequency will be 1 kHz.

If I change the time to 0.5 ms, the result will be 5V for 0.5 ms and the rest is 0. (The second cycle will not start after 0.5 ms, so the frequency is same 1 kHz). Strange!

How do I increase the frequency of the voltage source?


Question: Programming on Raspberry Pi device?
Answer: I have been programming for more than 40 years, and while c(and its successors) is my preferred language, since getting a Pi I have been using Python. If you know java this should not be too different, but I can recommend "Learning Python" 5th Edition.

You also asked about editors.
The Pi has IDLE, which is a Python IDE.
I strongly recommend Geany, which is easy to use.

Both of these are GUI, so if you are developing remotely you should use VNC (install tightvncserver on the Pi).

You don't mention what laptop you are using, but Mac, Windows and Linux all have support, but details differ.