Use the trapezoidal integration method using Excel and double integrate.

If you interested in the overall integral and not individual points, be careful with the integration results as integrations need a constant to be added to the result.

If you are looking at alternating acceleration (eg vibration), make sure your raw data doesnt have a DC offset. If not, force it to have a 0 mean value. Otherwise your displacement will shoot to an unrealistic value over time.

Alex.