Hi McLoz,
Wow, thats a whopper rose!
Sometimes roses just reach for the stars and put on a huge growth spurt of green stems, especially if not pruned each year.
Don't worry pruning it will not kill it.
You do need to prune it back to size to persuade it to grow into a more bushy open habit. The first step is to locate the graft. This will be a knobbly bit just above ground level. It will feel like a woody knot. Then remove any growth shooting up from beneath these as that's not the true rose. So we want to remove that growth that will suck the energy out of the grafted part.
You can see the graft as the brown knobbly bit below the green growth in the picture below.

The next part is to take back all other stems to about 6 inches above the ground. It will feel brutal but trust me it will work. Then next year you'll notice those stems that are left will then start to proud buds which in turn allows a more open floriferous branch network to form. With your rose, it will take a few years to get back into shape but patience will be rewarded. Using liquid feed when in flower/leaf and an autumn mulch of organic peat free compost will help get it back on its feet!
You can watch my rose pruning guide or read more here.
https://youtu.be/-Occ2WuIBnU
Make sure all cuts in subsequent years are at an angle away from a bud or node.

Happy pruning!
Lee
Hi McLoz,
Wow, thats a whopper rose!
Sometimes roses just reach for the stars and put on a huge growth spurt of green stems, especially if not pruned each year.
Don't worry pruning it will not kill it.
You do need to prune it back to size to persuade it to grow into a more bushy open habit. The first step is to locate the graft. This will be a knobbly bit just above ground level. It will feel like a woody knot. Then remove any growth shooting up from beneath these as that's not the true rose. So we want to remove that growth that will suck the energy out of the grafted part.
You can see the graft as the brown knobbly bit below the green growth in the picture below.

The next part is to take back all other stems to about 6 inches above the ground. It will feel brutal but trust me it will work. Then next year you'll notice those stems that are left will then start to proud buds which in turn allows a more open floriferous branch network to form. With your rose, it will take a few years to get back into shape but patience will be rewarded. Using liquid feed when in flower/leaf and an autumn mulch of organic peat free compost will help get it back on its feet!
You can watch my rose pruning guide or read more here.
Make sure all cuts in subsequent years are at an angle away from a bud or node.

Happy pruning!
Lee