Jostaberries

Can anyone help me with advice on pruning the above bushes, ours are about 6 ft tall and very 'bushy'.  We have noticed that the berries were smaller last year so we were wondering if lack of pruning may have been a factor.  Any advice would be appreciated.

I googled it and came up with a few surnames and a town in a Dungeons and dragons game...

I think that might be Jostaberry?

Josterberry :

Get yourself a pair of loppers (you won't need secateurs)

Start around the base of the bush and lop out any branches that are growing outwards or near to the ground.  This will give a more upright growth.  Try to thin the centre out a bit and remove badly crossing branches.

When you have done that stand back and look at it to see what needs shortening down so that you can pick the fruit.  Be careful not to prune leaving stumps at head hight, it's easy to walk into these and hurt your eyes - leave them longer and unpruned and they won't be a danger.