Why Germany did not up-gun its old pre-dreadnoughts

Did Germany plan to replace the Deutschland-class pre-dreadnoughts' guns with larger weapons?

No; larger guns would not make the obsolete ships competitive and were not worth the cost for training-oriented hulls.

The existing eleven-inch guns remained adequate for threatening cruisers. Against a modern capital ship, however, a larger weapon would not compensate for the old hull's wider deficiencies. By this stage the pre-dreadnoughts were most useful for moving recruits through training. An expensive rearmament would therefore consume time and money without changing their realistic combat role.