Japonica trimming

thomas.richards2dN4uPwTo

New to gardening. We have a japonica that needs some TLC.  Includes a white stalk at the top of one of its trunks (or whatever the correct term is) that from memory had its flowers from last year. Unsure if should remove this.
It hasnt grown much taller and dont want to remove what might be its core that prevents it growing taller.

K67

You need to clear a space around the trunk it needs to breathe without competition from other plants/weeds. No-one  likes being squashed together plants aren't any different especially when young and their root system is developing.
If the leaves are going yellow it usually points to too much sun, they prefer shader spots.
You are correct that it's an old flower stalk it will normally go brown but you can carefully snap it off as the new leaves grow from the top and older leaves underneath will die off.
This is my 3/4 year old plant and it look a bit greener than yours but some leaves aren't great and contrary to what I said it is squashed in with other plants but area is weed free.
I give it a mulch of bagged manure every spring keeping it a few inches away from the trunk, other than that I ignore it! 

thomas.richards2dN4uPwTo

Thanks for the advice. It is in direct sunlight. I thought it might of enjoyed the sun more being from a hotter climate. But can see now why its maybe gone more yellow.
Guess better get my spade out!

Pianoplayer

If it's any consolation, I did the same thing. I had to move mine just 1m over to get it in the shade, and it has been much better - I could almost hear it sighing with relief! So probably worth it.

Papi Jo

@thomas.richards2dN4uPwTo Welcome to our forum! 
There is no such plant as a "Japonica". Your plant is a Fatsia japonica,  aka Japanese aralia one of the many plants originating from Japan and thus with the "Japonica" epithet in their name. See https://search.thompson-morgan.com/seeds/Evergreen-Japonica-Shrubs