Partition, how to see it to erase files

[Firewing]

Ok, I am trying to use metamorph to install a theme for my swype keyboard... I have done this lots of times in the past but this time metamorph is telling me I need to free up space in my partition...where do I find that (like they root explorer, or what)...and is there anything I need to keep on it once I find it...
Thanks
Cara

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