What Arwu's saying in a nutshell is that if you highlight some sectors with right alt (so they're yellow) you can alter many of the properties of all those sectors at the same time. For example, you can change all their ceiling heights, floor heights, shades etc.. just by changing one sector.
And I see you've made two threads in a very short time, and from experience you're probably going to make a lot more. So if you run into another little problem that can usually be quickly fixed, please create a "Lynal's problems" thread or something along those lines where you can post all future tiny problems in one place and not clutter up the forums. Alternatively you could look to see if there isn't already a thread on the topic you're having trouble with. But if you do make another thread, please make it in the "help me" section, as this area is more for map releases and that sort of thing.
In addition, before asking help with a problem, you can try doing your own research by looking very hard at these resources:
1)
http://infosuite.duke4.net/ This is the mapping bible which explains a lot of effects and things very well with accompanying pictures.
2)
https://docs.google....S4ieZWWWTw/edit This is a document I wrote myself explaining some of the lesser known features of mapster32 which can really help speed up your mapping quite a bit (in this case it could have helped you raise all the ceilings at the same time instead of one-by-one, it has those sorts of tips across many aspects of mapping). It's aimed at beginners but it has some things even the pros weren't aware of.
3)
http://wiki.eduke32.com/wiki/Main_Page This is the official wiki for eduke32/mapster32. It'll be the last place you should look for mapping help though.
Since you're new here I welcome you to the forums and am looking forward to playing a map by you