You can take a maximum tax free lump sum of 25% of your total pot value. Have a look at page 12 of your plan guide for more info. It's available here: https://www.royalmailpensionplan.co.uk/ ... ts/library
If you are over 25% at the time of taking your pension, then any excess can be:
1. Taken as a taxable lump sum.
2. Used to buy an annuity if over £1,000
3. Commuted to provide more pension if under £1,000
Or else it is possible to transfer out either Flexiplan or Bonusplan to another DC pension arrangement before you take your RMPP/RMSPS benefits and then draw that down, which might be more beneficial from a tax point of view, depending on your personal circumstances.