Repaying some of mortgage

BROSTE

We have a standard rate mortgage with the YBS. It is made up of approx 50k endowment and 85K repayment. 2 endowments due to mature in 6 years. We allocated another investment against the mortgage endowment side at the time we took out the mortgage for approx 10k. This has now matured and we are not quite sure how to handle it with the mortgage. Should we advise YBS? Bearing in mind we still have about 14 years of mortgage left. We have approx 34k available. We would like to pay say 20k into the mortgage but we are really not sure if we are better putting it against the repayment or wndowment side or both. Can anyone help? The other 2 endowments look like they may bring in 32k.. should have been 43k. Obviously there is still another 6 years to go.
thanks