Either hack it all off or have plasterehttps://www.google.com/search?q=artex+removal+tool&rlz=1C1CHBF_en-GBGB846GB846&sxsrf=ALeKk02DHarYSkobSENFg-v0GQDUua9HPA:1592479369337&tbm=isch&source=iu&ictx=1&fir=JggL1SiZXdVZkM%253A%252CfdTyudRz0bmLpM%252C_&vet=1&usg=AI4_-kS6Ci3WCaMrggM2xNRfbmUu9QQIog&sa=X&ved=2ahUKEwjD-vv4n4vqAhUBQUEAHfwsADMQ9QEwAHoECAUQAw&biw=1680&bih=907#imgrc=JggL1SiZXdVZkM:
d over. or look here....
What the Builder said. If you do knock off any bits that stick out a lot just be careful as some artex used to contain a small amount of asbestos up until the 1990s I think it was.