how do i stop this

[yeyehboi]

why when i press space it decouples the top decoupler instead of launching/decoupling the bottom one? i cant have side boosters because of this and its really annoying

[Gargamel]

Your Question has been moved to Gameplay Questions.

In KSP, there's a phrase called "Check yo' Stagin".   You need to go back into the VAB and mouse over each item on the stage list.    It will highlight the corresponding part on the rocket.   Make sure everything is in the right order, from the bottom up (the bottom stage on the staging list will stage first when you hit the space bar).  You can move the items by dragging and dropping them in the list. 

[jimmymcgoochie]

It might be a little bit counterintuitive at first, but the staging system works from the highest number to the lowest, and from bottom to top on the list- just like a rocket detaches its stages from bottom to top. Bungled staging gets even the most experienced players sometimes so don’t worry about it too much, just hit revert and don’t tell anyone .

If you hover the cursor over a part, it will be highlighted in the staging list; the opposite is also true- hover over a part in the staging list and the part will be highlighted on the rocket. Make sure your decouplers fire at the right times to avoid dumping useful parts, lugging spent stages around or even decoupling while the stage is still burning and losing control of the rocket. Sort your staging out carefully in the VAB or SPH before launching as changing it in flight won’t be saved if you revert the flight or launch another one later. 

[king of nowhere]

make sure that the order of decoupling is set up properly in the VAB. often i make a craft perfectly calibrated, then i decide to add one piece, and that piece always get shuffled in the wrong place, and can cause funny moments if i don't remember to fix it.

[yeyehboi]

thanks guys for the help its fixed my problems!