Ok so you wanna free up some space on your MT Blog and your Recent Posts amount is getting to be a bit much. Well you can change it.
1.) Go into your MT Admin Side
2.) Click on Templates
3.) Click on Main Index
4.) Click inside the text box with the code in it and hold down Ctrl and then f. Type in Recent Posts as your search criteria
5.) You should be down in the code where the Recent Posts module is, scroll down below it a little till you see something like : MTEntries lastn="10" and change the 10 to a 5.
6.) Hit the Save and Rebuild button below.
7.) There you go your site should be changed to where now you only have five recent posts displayed instead of ten