On the HP 95LX, press (MENU) File Open and answer Yes when asked if you want to "Replace file without saving?" Then select the appropriate file name and press (ENTER).
On the HP 100/200LX, press (MENU) File and you are presented with following File menu:
File Management Options in MEMO: Graphic
The last two files you had open are listed at the bottom of the screen. Press 1 and the last file you saved will be loaded.