Hmm, OK. Firstly, it's cheaper than buying a new rod. As Christopher asked for advice on a rod he owns, not one he might be persuaded to buy, I consider it courteous to try and help him make use of it. Eight and a half foot cane or glass fly rods usually take a five or six line, so buying a six is a fair bet; the test I describe will enable him to ascertain the true line rating for when he buys his next line.
Secondly, he makes no mention of where he proposes to fish. If he intends to fish somewhere like Grafham from the shore he'll discover for himself if the rod is inadequate; chances are it will be, as you really need a longer rod of nine to ten feet for that type of fishing. However, if you've ever seen Hywel Morgan do one of his demonstrations, you'll know that he can cast plenty far enough with an old glass rod from Woolworths with half its rings missing. Fancy tackle is no substitute for ability.
But if he plans to fish streams, rivers or small stillwaters - collectively comprising about eighty percent of the available trout fishing in the UK, geographically speaking - an eight foot six rod is ideal and, as no long casting will be required, there's no need to replace it - as long as he can find what line it works best with.