There will be a $22 per minute fee for any video added to the profile even if you're removing/replacing older video. It is $22 for up to a minute of video, and $22 for up to each additional minute. There is a 4 second grace period at the top of each minute.
We would suggest breaking reels into individual clips. Casting directors have repeatedly stated that they prefer clips rather than demo reels.
Clips allow you and your reps to submit only the clip(s) that apply to the role to which you're submitting. This will also save you $$ as you won't have to routinely update a demo reel and re-upload it every time you get a new clip. You will be able to simply upload the clip and pay for just that footage.
You can use the "Create Clips" option in the Manage Media section of your account to break up your existing reel at no charge. Then you can upload the new clips as new footage. Here is a video tutorial that will take you step by step through the clip making process: