scale change

how can I change the scale of a dwg from AutoCAD 2013 version on 1'=1/4" into 1'=1/8" AutoCAD 2006?

Welcome to CADTutor. The changing of scale has nothing to do with the year of the software. Sounds like you have 2 issues, changing the scale, and possibly saving a 2013 created drawing to be compatible with 2006 software. Assuming that the drawing was correctly drawn at full scale (1:1) in modelspace, then you would likely be setting your scale through a viewport in paperspace. Here is what to do. Unlock the viewport and double click into it, to make it active. You can then set the new scale in PROPERTIES for the viewport. 1'=1/4" is the same as 1/48, and 1'=1/8" is the same as 1/96. Don't forget to relock the viewport scale once you have set it how you want it. To SAVE BACK to an earlier 2006 compatible file format from 2013, do a SAVE AS, and then from the FILES OF TYPE drop down menu select AutoCAD 2004/LT2004 Drawing[*dwg].

The versions of AutoCAD you mention have no bearing on a drawing's scale.

Was the drawing done "to scale" as one would do on a drafting board (manually)? If so you would scale the drawing by 50%.

Somebody has the scale factors backward. 1'-0" = 1/4" and 1'-0" = 1/8" would be magnification scales, 48X and 96X respectively.

Either the OP has stated the scales backward or you both have given the information as 1/4" = 1'-0" and 1/8" = 1'-0".

Per OP's criteria, you would scale by 2.

Perhaps the OP will clear this up?

I believe the OP has stated the scales backwards and we are really talking about 1/8"=1'-0" and 1/4"=1'-0" since both are well established architectural scales used in the U.S. Note that the OP hails from the state of California commonly referred to as "la-la land".

I stand by my original advice. Scale the drawing by 50%.