I was going to post this section at the end, but in case you're
one who likes to dig right in without reading all instructions first...
... BACKUP ... BACKUP ... BACKUP ...
I am sure that goes without saying, however, be certain to perform
a backup for BOTH blogs before you do anything. AND, be sure to
keep a local copy as well as one server side, at least until you are
1,000% certain everything finished without a snag...
Visit the Tools -> Export section in your theme 2 dashboard.
Download the XML file of your blog's content. This file should
contain your posts, pages, comments, categories, and tags.
Then, import that by visiting Tools -> Import on the theme 1
Choose "WordPress" when asked for the format and then simply
follow the instructions.
You should be asked to upload that XML file that you previously
created when "exporting".
Let me know if you need any further assistance.
Ooh, and if I didn't mention it already, be sure to BACKUP before
all else, LOL...