How to connect 4MHZ crystal oscillator to get 16MHZ
No, connecting them in series or parallel won't get you a higher frequency.

What you're looking for is a Phase Locked Loop or PLL. Here's a block diagram:



A Voltage Controlled Oscillator (VCO) generates the output frequency. This signal is divided and then compared to the input frequency in the Phase Detector. If the two frequencies aren't the same, the output frequency is adjusted. This is called a feedback loop: you feed the output frequency back to adjust it.

The Pre Divider allows you to multiply the input frequency with a floating point number. For example, when you want to multiply by 2.5=5/2, you first divide the input frequency by 2 and then multiply by 5.

There are ICs available that have a PLL implemented, like the LM565. On page 10 of the datasheet a typical application circuit for a ×10 multiplier is given:



By changing the voltage divider (the external IC) you can make it a ×4 multiplier.

Implementing a PLL will cost some effort and space - consider buying a new crystal.