TV amplifier question? Get better signal

I am trying to improve my TV signal.   right now I have an old (made in
1995) amplifier that is connected to an TV antenna (aprox 25ft high) mounted
on my house.   Right now I have RG59 Coax cable (75'ft)  which I want to
replace with RG6 cable.    My amplifier is rated at 2.5w and 0.025amp.    I
would buy a newer amplifier, if I thought it would help my signal.     I
looked at a new amplifier at Radio Shack and the rating system seamed to be
different now.    It was rated at 10dB and I believe it mention something
about frequency.   I assume the higher the db value means more
amplification.    Will a 9dB amplifier do just as good as a 20dB amplifier.
What is the highest value that would be safe for my TV?    They could not
explain it to me at the store.

Second question is about buying one of those omnidirectional TV antennas
that look like a flying saucer.     I believe they have a built in
amplifier.    If I bought one should I use it in combination with my old
indoor amplifier 2.5W?    Thanks a lot for your help.

Also, any other way to improve my signal (don't want to pay for cable)?
thanx