Increased speed through provider - disappointed in results (model CBR40)

I should start by saying, my husband set up the orbi and I know very little about it and I am not technical at all, so please if you have suggestions, be specific with step by steps and explain any technical terms - thank you so much in advance!! 

The kids will be livestreaming from home in addition to us working from home so I increased our internet speed today. The highest we could have gotten was 1 gb but apparently the orbi only supports up to I think 866 mb. So the next best option was 500 mb that I could upgrade to from 100. Before the upgrade, my download number on the speed test ranged from 79 to 114. After the upgrade to apparently 400 (not sure why they didn't do the 500 when that's what we discussed) has ranged from 152 to 188.

The internet provider has done speed tests on their end showing they're sending it out at 400 so the issue seems to be on my end with the orbi, according to them. 

Any suggestions of what I can try. I have read about changing channels (don't know how to or understand it or if that would help this issue!) 

I see my Orbi firmware version is V2.3.5.12_1.0.8

The CM firmware version is V1.01.05

I see the Wireless settings:

2.4G Channel Auto (11)

2.4 G Mode up to 300 Mbps

5G Channel 36+40+44+48(P)

5G Mode up to 867 Mbps

Not sure what other information would be helpful. Again, thanks in advance for any attempt to help me. I spent hours and hours on this today with my internet providers speaking with several different people both through live chats and on the phone to no avail.