boot partition too small

[Stuart McGraw]

I made a mistake when I installed my Fedora 21 system -- I
specified a /boot partition size of 200MB rather than the
recommended 500MB -- and didn't notice my mistake until
I had too much time invested in the install to redo it to
correct the size.  (I am using plain vanilla ext4 partitions
not lvm).

When I tried to do a yum upgrade today (which includes a
new kernel) it failed with a message that my boot partition
space was short by 6MB.

What can I do to fix or mitigate this problem?  There are
currently 3 kernels and a forth (the biggest) with "rescue"
in its name.  Do I need that if I create a rescue CD to
boot from?  Can I arrange things to keep only one extra
kernel instead of two?  How?

Suggestions or pointers to information couched in simple
terms (I haven't had to deal with any of this boot stuff
in 15+ years) will be very much appreciated.