The aaltoseries class can be used in LyX as well. However, it requires some preparation before you can use the class. In this page, short instructions how to use the aaltoseries class in LyX are given.
First, you need to install the aaltoseries class file, aaltoseries.cls, and the aaltologo package file, aaltologo.sty, "to a place where TeX can find them". This means that you need to put them either in the TeX directory structure, in the user's local TeX folder, or in the folder where your (main) document file is located.
The location of the two first options are operation system and LaTeX distribution dependent, so you are advised to google for the locations of your system. Moreover, note that the second option may be or may not be in use in your system. The third option always works, but it requires that you put the abovementioned two files in every folder you have documents that use them.
You find the LyX layout file attached to this page (direct link). You need to put that in the public or local layout folder of your LyX system. Again, the location of these folders depend on your system. Typical locations for these layout folders can be found at LyX Wiki, http://wiki.lyx.org/, under the "group" Layouts and by following the links of related instructions.
After you have done both abovementioned tasks, you need to reconfigure LyX. It can done via a menu command, see the LyX Wiki. Then, restart LyX, create a new document, and set the document class in the document settings to aaltoseries, see the LyX Wiki.
You can typeset ordinary text as well as chapter, section, etc. headings using the normal approach. However, since the aaltoseries class provides many special class-specific commands, they are not supported by LyX as is. You need to give them in the TeX mode (the evil red box, see the LyX wiki) following the instructions found in the documentation of the aaltoseries class.