Di2 Adjustment

[MrTickle]

Hoping someone could point me in the right direction.

I have a bike with Shimano Di2 groupset. When in the large cog on the crank, all gears are sweet as a nut. However, when using the small cog on the crank I get some clicking and occasional unplanned gear changing in 3/4/5th.

Anyone know how easy it is to adjust the Di2, or even better a knowledgeable Di2 tuning shop in the South Cheshire area?

Thanks.

[MrTickle]

Thanks for advice - I will look up the manuals online