Standard practice for cashing out bonus points - you should cash out all bonuses and VIP points on your poker rooms 1x per month.
At the end of each month, you will get a reminder to cash out your points on all the poker rooms. You can do it more often, if you wish to in crease your BR, and if it makes sense.
As a standard, good practice is to cash out at 1x monthly, so don't be lazy and go after the cash.
The bonus points are part of your BR, they are simply a part of rake that you have paid, which is now returned to you as a "bonus" by the poker room.
See below for a few examples on how to cash out bonus points on different rooms. If your room is not shown in the example, get familiar with the bonus point system on your room (usually you will find options to cash out the points in the "cashier", "reward", "VIP" or "store" sections of the poker room.
IMPORTANT: You will always have several options available. Always buy the biggest amount of cash you can get with your points. Then buy the next biggest which you can still buy. Most rooms have a system where it pays to always buy the bigger award at once, do not buy many smaller chunks, if you can avoid it.