Value-at-Risk of a distribution?


I have returns data for 2 assets for a 10 year period.

I want to determine the Value-at-Risk for the distribution of this data. I have plotted at histogram, but I dont know how to determine the Value-at-Risk (VaR) value for the distribution.

I know how to determine the VaR for parametric distributions, but my data is simply historic data.

Can anyone help?

Any help will be appriciated!!
Actually, what I have is disribution of returns and would like to find out the z-value like you find for a normal distribution, except that this distribution is not normal. Therefore, i cannot use a normal z-table.

how can i find this value for a non-parametric distribution?