Translation:No thanks, we will change it ourselves.
Honestly, your rigour concerning the difference between "this" and "that" is so annoying. I always make mistakes because of bu, su, şu, o and this,that... There is no big difference between
"No thanks, we will change that ourselves." and
"No thanks, we will change this ourselves.", especially without context.
Try to remember it like this:
"Bu" is generally used to points thing that is very close to you "Şu" points objects a little further. "O" object is farther ahead than "bu" or "şu".
Consider 3 cars crashed eachother and you are describing them to the policeman. You point the car closest to you and say "bu araba", then you use "şu araba" for the car next to it and for the car that is in the distance you tell "o araba".
Same relation also applies their plurals: BUNLAR, ŞUNLAR, ONLAR
This is NOT a strict grammer rule but how Turks usually use these words in daily life.
That is because you do this automatically in your native tongue, but have to think about it when conciously translating a language that you have yet to understand. We do this, that and the other (bu, şu, o) is different from this, this and this. The fact that you are being caught out means that you will be more careful when reading Turkish sentences. English has a plethora of words we can choose from to destinguish sound intonation. With Turkish the grammar provides the destinction. 'Bizim ev' means nothing without evimiz. Verbs mean nothing without the agglutination on the end. Şu, bu are destinguished by their sounds. If you read out loud the sentence, then your ear can help the brain. If you just think the sentence, and your concentration is not 100%, then you make assumptions. I too make mistakes. I read oradaki and by the time I write the English word I have written here instead of there. If you have gotten this far into the course, then you are frustrated by not being able to pick things up quickly. You have to remember that, as you progress, the course gets more complex and more demanding. It acts as a natural brake on your progress. If you are doing 50 questions a day like me, then perhaps you should do 30 to take the pressure off you. Trying to keep a streak going when the sentences are tougher could be detrimentel psychologically, especially when you have other commitments:D:)