You can only book rooms available for points. Some hotels allow you to book upgraded rooms/suites for additional points. Those hotels will show the upgraded room options and the points needed to book. Others limit you to a basic room. If the room you want is not available for points, you can always reach out to the property and ask if they will make the room available to you for additional points. Some people have reported having success while other have not. Personally, I've had success twice (once to a 2 br at an RI and once to a suite at a FS) but failed twice, too.
Examples: You can search Marriott.com and find the following: Wailea Beach Resort Maui, night of Aug 21, you can get a regular room for 40k MR points or an oceanview room for 60k MR points. For the same night, the JW Buckhead Atlanta will only give you a regular room for points. The hotel is not offering suites for points.