I've taught a lot of world class athletes how to surf.
When they get out of the water after their first session, they all say the same thing:
"&%$#", that was a lot harder than I thought it would be!"
If you are relatively new and are thinking of downsizing... I caution you from taking too big of a step down. 
4, 6 inches... at the most.

There are many other variables that determine how the board will ride.
Width, thickness, width and thickness distribution, rocker, fins, how many, placement, size, template, type of foam, glass, weight, flex, finish, and more.

Most beginners, or surfers that are relatively new, think they are good enough to take a big jump in size.
If you are taller, heavier, and a little older, all these factors matter in what type of board you should ride... if you want to really enjoy your surfing experience.

I started surfing in 1966.
I was XXL. 

By the time I was in High School, I was 6'4 and closing in on 200 pounds.
The shortest board I ever owned was a 6'3 Twin Fin I shaped my Junior year in High School. I was 6'4 and weighed 200 lbs.
I aspired to be a Pro.

I got 2nd in the SD High Surf Championships in 11th Grade.

It became quite apparent to me, by the time I turned 20, that competitive surfing wasn't really for larger surfers.
In 1972 I entered a Pro contest in Huntington Beach.
My first heat I thought I did pretty good.
Got a lot of the better waves.
Surfed solid, I thought!
I came 3rd out of 4.

Look at the average pro these days.
There are a few guys maybe 6'3, maybe 210. 
But they are young. In their 20's.
Started surfing at a very young age.
Most of them are well under 6 feet tall. 
Usually weigh in between 155 and 175.

I know/hope you don't have these types of aspirations.

My parents moved to Oahu in the Fall of 1970.
Over 60 trips to Hawaii starting in 1970.

In my 20's I rode between 6'4 and 6'10.
'In my 30 s, every couple of years or so, my boards crept up in length.
Got a little wider. A little thicker.

I was able to start traveling.
Surfed a lot of perfect waves.

First trip to Australia, Gold Coast, January 1974.
Again in 1980. And 1982.
West Australia, first trip was in 1983.
I've lost track of how many times I have been since.
Over 50 trips to Tavarua, starting in 1986.
Over 20 trips to Indo starting in 1999.
Around the world many times.

In my 40's, my go to boards were approximately 7'4 and when I was closing in on 50, my boards were between 7'6 and 7'10 for a short board.
Well over 22.0 inches wide and over 3 inches thick.

I was still a good surfer.
I am very large as far as shapers go. 
Most have a difficult time scaling up their designs. 
Not all, but it's rare.

For me, it's natural. In my "Genes" so to speak.
You started surfing at a relatively older stage in life.
That's a challenge in and of itself.

If you really want to have fun, go down in size slowly.
Once again, I would recommend 4 to 6 inches at the most.

Happy to help... but you gotta

Trust your Shaper!

Rusty