Pruning erect blackberries
The fruiting canes that had fruit on them this year should be removed.
You do not say if you are using a trellis or not.
If there is no trellis the primocanes that grew from the ground this spring should be tipped at 3 feet soon after they reach that height (in June and July).
This will cause the canes to branch. These lateral branches should be cut back to 12 to 18 inches in the early spring before growth begins and the laterals will bear most of the fruit. longer laterals will have more smaller fruit than sorter laterals which will have fewer larger fruit.
Trellis training systems depend on the trellis height but generally the primocane is tipped when it reaches a wire and later loosely attached to the wire