Changes

From center take city bus #27 until it intersects with the 12. Lots of room for cars to pull over and ther is a Gendarmeria stop another 5-10km further if you can get to that then a ride the rest of the way should be easy.

From the centre, it should be about a 20 minute walks towards the Puente Internacional. Lots of crappy shops and a choripan place to spend the last of your fairly worthless pesos. Busy crossing. No bag searches or heavy questioning. You can not walk across the bridge, but it is easy enough to sneak on the public buses that cross. Tell them you lost your ticket if they enquire. On the Paraguay side, specify you are there for more than a day. Again, you can sneak on the public bus. This will take you past the bus station, public plaza and then further north. When it turns West, get off and follow the main route north towards Asuncion. Pain in the arse to hitch out.