Your DC pension with Aviva is just a pot of money that benefits from additional contributions from the tax man and your current employer. When you come to access it, you basically have 4 options(taken from this informative link
1. Take your whole pension pot as a lump sum in one go. A quarter (25%) will be tax free and the rest will be subject to Income Tax and taxed in the usual way. Bear in mind that a large lump sum could tip you into a higher tax bracket for the year.
2. Take lump sums as and when you need them. A quarter of each lump sum will be tax free and the rest will be subject to Income Tax and taxed in the usual way. Bear in mind that a large lump sum could tip you into a higher tax bracket for the year.
3. Take a quarter of your pension pot (or of the amount you allocate for drawdown) as a tax-free lump sum, then use the rest to provide a regular taxable income.
4. Take a quarter of your pot as a tax-free lump sum and then convert some or all of the rest into a taxable retirement income (known as an annuity).
You may be able to do what you want to do(flexi-drawdown) via Aviva. But some providers don't allow full flexibility on all of their products, so you'll have to find out yourself whether you can do that with your pension or not. And if not, then transfer your cash to somewhere that does.
As stated earlier, the only option with your RM pension is to take up to 25% tax free cash, and an income for life.
Pensions are a bit of a minefield, so I would suggest you do a lot of homework and make sure you're doing the right thing for you and your family, not just now but think well into the future as well.
Also get yourself a state pension forecast
, as that will form an important part of your income for the rest of your life. Depending on circumstances, you may or may not get the 'full' amount, currently £168 per week.