I have a pension that was opened with a previous company, I am no
longer paying into this pension.
I am only 27 and would like to use the money from the pension now.
Can I cash the pension in and get access to the cash?
How do I do this?

If the Pension Scheme Rules allow you to take an early pension as
early as age 27, then yes.

But, more likely, they will only allow you to take an early pension
at, say, age 60.

Then, typically, you can generally only take (say) 25% in cash; the
balance is used to buy an annuity.

The rules are very complicated and you should discuss the options with
the Pension Administrarors.

My guess is that you can't.