For better PC performance optimization may we recommend that you:

• Use 1024 x 1024 texture resolutions when editing character textures
• For performance considerations, please do not use higher than 1024 x 1024 resolution when editing character textures. Unless you wish to preview, or do final export, which you can then choose a high resolution like 2048 x 2048. 

To do choose a high resolution, simply:

1. Select the character 
2. Open the Modify panel, click on 'Activate Appearance Editor' 
3. Select 2048 x 2048 from the drop-down menu. (Do this for both body and head)

93% of original size (was 542x16) - Click to enlarge

93% of original size (was 542x16) - Click to enlarge