To sell or not to sell endowments?

Beemer

Hi,

I have three endowment policies that I have had for a number of years. One of them has stated that it will not reach its intented value (although I don't think I have a claim).
I am about to reach the end of my current mortgage fixed term and one recommendation was to sell all three endowments and move to a repayment mortgage.
I know nothing about selling endowments but believe the one that may not reach its full value at majurity will cost me to sell it.
I feel that there are some pitfalls here and uncertain as to whether I should sell these policies.
Appreciate its a big subject but any advise on what too look out for or consider or even questions to ask would be very much appreciated.
Thanks
Richard