Originally Posted by Poguemahone

You need a crank remover. A specialized tool that screws into the treads on the crank, and then pushes the crankarm off the bottom bracket spindle. That looks like a late seventies UO10. The stock cranks are stronglight, but they take the standard 22mm remover (some older stronglights take a larger diameter crank remover). Odd 122 bolt circle diameter on the cranks, can be hard to replace. Depending on frame vintage, the bottom bracket on these bikes is threaded either French or Swiss, the later being tough to replace. Fortunately, the stock bottom bracket is pretty bombproof; just grease it up with fresh bearings and you should be fine.