I have removed my Juwel filter without any problem whatsoever - it took less than 5 minutes and I did not have to strip or empty the tank
Just remove approx 50% of the water.
Remove all inner filter sponges & heater (and keep in the 50% water that's been siphoned off; while you remove filter).
Make sure all electricity to your tank is off.
Get yourself a "snap-off-blade" Stanley knife.
The Juwel Filters have 4 blobs of 1" silicone on each side attached to the tank (back & left).
Start with the top front blobs and use the knife in a "sawing" motion to slice through the silicone. Then do the back top blobs.
Then the bottom front.
By this time you can almost just gently pull the filter forward, enough to reach the back 2 blobs (side and left).
Once filter is removed, you can use a (unused or fish dedicated) pot scouring pad to remove any remaining silicone.
Note: Take great care not to let the blade slice into the actual tank seal silicone !
Place all Juwel sponges in new external filter, plug and ply and bob's your uncle
Ps: you can still use your internal Juwel heater - just buy a
Heater Guard.