lyx_mirror/UPGRADING

How do I upgrade my existing LyX system to version 1.1.6?
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If you upgrade from version 0.12.0 or 1.0.x, you shouldn't have 
any problems.  However, in the source we have begun a transition
to use ANSI C++ more and this can make it hard or impossible to
compile LyX on old or non-conformant compilers. If the compile is
successfull everything should be just like in 1.0.4. Just run
"make install", and it will automatically update the necessary
files, provided that you install LyX the same place as
an existing version.

Document transfer
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In general, you don't need to convert any documents saved with LyX
v0.10, v0.12.0 or v1.0.x to use them with LyX v1.1.6.

LyX v1.1.6 can read all documents saved with lyx-0.12.0 and later correctly.
Documents saved with lyx-0.10.x are read correctly up to the old math 
mode, which is not supported anymore. If you have documents with such 
math formulas, you convert it using the program COLD, written by Preben 
Rhandol. COLD can be found at:

  http://www.pvv.org/~randhol/lyx/COLD/
  ftp://ftp.lyx.org/pub/lyx/contrib/

or at one of LyX archive mirror sites listed in README.

Documents saved with LyX version 1.1.6 can be read correctly by 
LyX v0.12.0 and v1.0.x, except for new and a couple of changed
features. A notable exception is the tabular format, which has changed
in a major way in 1.1.6. No older versions of LyX are able to read
this new inset.